Ja'far is an average-sized man with pale skin, short white hair and black eyes. He also has freckles around his nose. He wears a long drape that covers his entire body, and a green Arabian keffiyeh on his head. He always carries around his red wires, which is his Household Vessel, Bararaq Sei. When enraged, his eyes change into eyes that resemble those of a snake and turn gray. When Ja'far's hair is shown, it is always wild, as has been like this since he was young.
In certain instances, Ja'far's legs can be seen to be marked with two large, almost stitch like scars, which were originally confused with the jagged seams of his young assassin trousers in their first appearance. He still has those scars as an adult. When J'far undergoes Household Assimilation, he has scales forming on his chest. 
After three years, Ja'far no longer wears his keffiyeh, instead just the small red gem is wrapped around his head. He no longer wears his casual clothes and instead wears his white-sleeved button shirt with a dark vest, dark pants and shoes and what seems to be a cape or cloak on his left shoulder while a white cloth with a shoulder guard is on his right. His hair also seems to have gotten a little bit longer. Alibaba notes that Ja'far doesn't seem to have aged despite three years passing, something he seemed to take a bit sadly before displaying a smile to the prince.
He reverts to his original appearance at the start of the series at the end of the series. 
Ja'far is a serious person, who gets angry easily. He is most often the voice of reason when Sinbad is doing something outrageous. He tends to scold Sinbad a lot, despite Sinbad being his King, older, and stronger than him.
When provoked or angered, Ja'far shows a whole different side to himself. He was easily willing to kill Cassim when the latter opposed Sinbad. Another time this happened was when Judar called Ja'far a "small fry" and told him to step aside because he had some business with Sinbad. Enraged, Ja'far was going to use his Household Vessel, Bararaq Sei with his full strength, but was stopped by Sinbad before he could do so.
However, despite his short-tempered nature Ja'far is shown to be mostly kind and polite towards others (except for those he sees as an enemy). He cares deeply about the people he loves and is shown to have a soft spot for children, as he treats them almost like a mother would. He is also a workaholic, to the point that he would still be working even when he's asleep.
Ja'far was born into Parthevia's undercover unit, the assassins Sham Lash, and at one point became its leader. At the age of six, he was forced into killing both of his parents.
After the dungeon of Baal was conquered by Sinbad, Parthevia's Emperor ordered his troupe to track down and capture Sinbad and take out Drakon if he became troublesome. The Emperor did not want Sinbad dead but sought out the troupe because they knew sensitive information that the soldiers did not, and were excellent at dealing with combat. Despite the Emperor's wishes, Ja'far tried to assassinate Sinbad for unknown reasons. He failed in the assassination and decided to serve him as a vassal.
Little is known about Ja'far's history, but it is evident that, from a young age, he was under intensely abusive treatment, which would have most likely warped his ethical reasoning and his physical body.
Since his assassin days, Ja'far has apparently become quite tame and serious. Sinbad remarked that Ja'far's eyes were always rogue when they'd first met. Over the course of their acquaintance, Ja'far has apparently grown very close to his King, to the point where he is the only character to have nicknamed Sinbad, calling him always by "Sin." There appears to be a respect between Sinbad and Ja'far, as Ja'far was entrusted with the care of the entire Kingdom of Sindria while Sinbad was away.
Ja'far and Masrur are at a hotel, waiting for Sinbad to return. When Sinbad returns with Aladdin and Morgiana, Sinbad explains the situation to him and Masrur. Ja'far offers to pay for Aladdin and Morgiana's room. As they walk to their respective room, Ja'far asks Sinbad if he got all his luggage stolen again, to which he answers yes. Ja'far exasperatedly asks if everything got stolen including all his metal vessels, to which he also answers yes. Ja'far asks Sinbad, when will he become aware that he was born to be "King". Then, he calls him King Sinbad. Sinbad tells him not to expose that.
Ja'far and Masrur are present in the meeting between Sinbad and the Balbadd's king, Ahbmad Saluja and Balbadd's deputy king, Sahbmad Saluja. The meeting is about why Balbadd has broken off trade with Sindria. They hear about the Fog Troupe from the two, and soon Sinbad declares that he will, by himself, destroy the Fog Troupe.
Ja'far then has lunch with Masrur, Sinbad, Aladdin and Morgiana. Sinbad formally introduces Masrur and Ja'far. Aladdin introduces himself and summons Ugo, which surprises Ja'far. Sinbad is also surprised and states that Aladdin is a Magi. Knowing the power that Aladdin wields, Sinbad asks Aladdin to lend them his power in capturing the Fog Troupe. Ja'far protests this, saying Aladdin is just a kid. Sinbad says that age doesn't matter, but what matters is the capability of facing the Fog Troupe. Ja'far eventually submits and proceeds to explain the plans to everyone. He explains that the Troupe's are seen when there are fogs and targets the country's treasury and rich citizens. He also tells Aladdin and Morgiana about the new recruit to the Troupe that everyone calls, 'Wonderman Alibaba'.
Ja'far is next seen with Aladdin and Morgiana, helping them in fighting the fog troupe. He along with Aladdin and Morgiana, are attacked by the Fog Troupe. Ja'far uses his wires to attack the troupe and states that he is not from Balbadd, but he has reasons to capture them. However, Ja'far was binded by Cassim's weapon, Kokubaku Mutou.
When they went back to the hotel, Ja'far explains to Sinbad about the economic problems in Balbadd and that it was caused by paper money called "Juan" that were issued by the Kou Empire. Later he is present when Sinbad is listening in on Alibaba's story and when the Fog Troupe attacks their room. Ja'far attacks back using his wires. On the roof Ja'far shows disbelief and confusion when Sinbad offers to join the Fog Troupe after defeating Alibaba. He protests that it would make matters more complicated, in which Sinbad replied whether Ja'far was "not human", leaving him completely speechless and defeated.
When Cassim bad-mouths Sinbad, Ja'far is enraged and attacks him with his wires. He states that Cassim has no idea what Sinbad had been through, and is prepared to kill him. However Sinbad stops him by grabbing his blades, which injured his hand. Ja'far is shocked and immediately apologizes for injuring Sinbad, in which he replied that it was "Ok".
Ja'far then looks after Aladdin when he is unconscious. When Black Rukh is taking over Balbadd, Ja'far wants to help Sinbad in the castle, however, as he says to Masrur, he cannot abandon the people that are in panic. He is next seen attacking Banker with Bararaq Sei after Masrur knocked him down, allowing Sinbad to finish him off.
Ja'far is first seen as he greets Alibaba who is enraged that he was taken away from Balbadd. When Alibaba asks whether Sinbad had any rights to confront the Kou Empire, he states that Sinbad had "none whatsoever", but that won't stop him from trying to help Alibaba and Balbadd.
After the 6 months time skip, Ja'far is next seen as he greets Sinbad after his return from the Kou Empire. He asks what happened and Sinbad informs him of the agreement with the Kou Empire's Emperor. He also informs Sinbad that at first Aladdin and Alibaba were depressed, but they had gotten more cheerful and started eating well (in which in the manga, causes them to grow fat).
When a Southern Creature attacks Sindria, he stands alongside the rest of the Eight Generals and watches as Yamraiha and Sharrkan defeats it. During Mahrajan, Ja'far is first seen when he hits Sharrkan for bullying Masrur. Sinbad then assembles the Eight Generals and officially introduces them to Aladdin, Alibaba and Morgiana. He states that Ja'far is a parliamentary official, and that he is an expert in a unique assassination technique. Ja'far then later asks Sinbad whether he had resolved the situation with Princess Kougyoku in which Sinbad seems oblivious. He shows great concern that Sinbad had played with the princess, which could potentially cause a war between the two countries. He is relieved when Sinbad replies that he didn't do anything.
However when Prince Hakuryuu and Princess Kougyoku arrives at Sindria, Ja'far is shocked when the Princess accuses Sinbad of "defiling" her. When Sinbad tries to prove his innocence, he along with the other Generals shows their disbelief. He states that although they respect their King, they know well about his bad habits when he's drunk. According to him, it has happened before when Sinbad was drunk and ended up having "many local wives" in the morning. Also, Ja'far points out that in Balbadd, Sinbad lost all his belongings, including his metal vessels, due to him being completely drunk that he passed out. With shock at his Generals' disbelief, Sinbad states that Ja'far was looking at the eyes of an assassin, like their first meeting.
When Yamraiha uses her magic to show what happened that night, Ja'far covers Aladdin's eyes as children should not see what supposedly happened. However, it is shown that nothing occurred during the night, which causes Ja'far and the other Generals to apologise for not trusting their King. When Koubun Ka is revealed to be the culprit behind the misunderstanding, Ja'far glares at the man and spits at him.
Although Sinbad tells Aladdin, Alibaba, Morgiana, and Hakuryuu to conquer the dungeon at Torran alone, Ja'far sends Sharrkan, Masrur, and Yamraiha to the island as well for safe measure.
Ja'far is first seen as he reports to Sinbad that Yamraiha, Masrur and Sharrkan has reached Aladdin and the others. They are suddenly interrupted as Yamraiha's barrier around Sindria is broken, which allows Judar to enter Sindria. Ja'far then joins Pisti and the other guards to confront Judar. He attacks using his Household Vessel, Bararaq Sei, but was thrown against a wall by Judar. Ja'far is angered when Judar calls him "small fry" and says that he wants to speak with Sinbad. Ja'far's eyes has taken a sharp look, resembling a snake, which is shown when he is furious. He attempts to attack Judar again, but is stopped by Sinbad. Ja'far complies with Sinbad's order and stands by his side silently as Sinbad and Judar talk.
He is next seen during the banquet Sinbad threw to celebrate Aladdin and the others' return. Ja'far leads a confused Koubun Ka away, giving Sinbad freedom to approach Princess Kougyoku. After Sinbad's talk with Kougyoku, Ja'far approaches him revealing that Sinbad is trying to gather power for Sindria. He is confused when Sinbad asks whether he had become "a sly person" and remembering the adventures they had when they were younger. Ja'far then replies that Sinbad is indeed a sly person and has "become what [he] didn't want to be". However he adds that it is the path Sinbad has chosen and he can only move forward. Ja'far pledges his loyalty and says that he will follow Sinbad until the end. Ja'far then accompanies Sinbad to approach Hakuryuu to try and persuade him into being their "power" as well. However the banquet is suddenly interrupted by Ithnan. When Ithnan's clones attacks them, Ja'far destroys one of the clones. However this only makes the clone's blood splatters into Sinbad, allowing Ithnan to curse him along with Alibaba.
Ja'far asks Yamraiha if Aladdin was able to enroll at the Magnostadt Academy without problems. Proudly, she tells him she is sure that Aladdin will be selected for the first Kodor, the highest level at the academy.
After Pipirika helps Alibaba arranged an appointment, Ja'far is shocked that Alibaba is alive. Ja'far learns from Alibaba about Yunan preserving Alibaba's body. He remarks that Sharrkan and Yamraiha were the ones who grieved for a long time. Then, he helps Alibaba arranged an appointment with Sinbad. He boasts how he is Sinbad's right hand man.
Ja'far is a trained assassin. Ja'far is proficient in using rope darts to ensnare and stab his opponents.
- Remote Control Blade: Ja'far throws his darts and they cross each other to constrict his opponents. This is a special assassination technique of the Sham Lash.
- Bararaq Sei (Twin Snakes Rope Darts): Ja'far's Household Vessel. It takes the form of his rope darts that he changes into the form of twin snakes to ensnare and bite the opponent. Its attack has enough power to destroy the Borg of Ithnan.
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Ja'far first met Sinbad when he was still an assassin. He tried to assassinate Sinbad under the orders of Parthevia Empire. Though, after the event in Valefor Dungeon, he decided to trust Sinbad, gave up on the path of being an assassin and followed him. He's close enough to nickname him "Sin".
Ja'far also shows loyalty and trust towards Sinbad. He is often seen to be accompanying Sinbad and took care of much official business. This trust seems to be reciprocated by Sinbad, as Ja'far was also tasked to be in charge of Sindria while he was away.
However, it seems that Ja'far doesn't fully approve of Sinbad's actions as he stated that he will never be used to Sinbad using excuses such as "for the sake of the country.... to tie down other people's life". After three years of time skip, the two are shown to work in separate places and they seem to rarely meet with each other, as the two are busy with their own work. Ja'far does talk with Sinbad as a friend and suggest to him to apologize to Kougyoku after Kougyoku's declaration to leave the International Alliance as well as asking him to shoulder the burden.
After three years of the timeskip, the two are shown to still work in the same company. Ja'far stated that he is Sinbad's right hand, and he is most likely responsible for Sinbad's schedule, as he also told Sinbad his next meeting would start soon. When Alibaba and Aladdin went to meet Sinbad, Ja'far was seen beside Sinbad in his office, and is seen with Sinbad several other occasions, such as when Sinbad had a phone call with Alibaba. He also still has his concern for Sinbad, shown when he went to Sinbad's office late in the night, and tried to convince him to apologise to Kougyoku. Ja'far also tried to help him by saying Sinbad shouldn't run from the present. He was angered and sad when Sinbad said he knew a method to reshape the world, but may die, showing that Ja'far cares deeply about him.
The two seem to be close, working together and understanding each other well, being Sinbad's first subordinates. Ja'far is also the one who taught Masrur to read and write, though Masrur would usually attempt to escape when he is away to get more work for Masrur to do.
Ja'far gets along with them, but cannot stand when they constantly fight over what's better, sword or magic. He also mentions to Alibaba that the two were lost after his death and would have been jubilant to find out he's alive.
Ja'far seems to have a soft spot for Aladdin, seen when he tries to keep Aladdin happy when he brings up Ugo, and when he covered his eyes during Sinbad's supposedly evil deed towards Kougyoku (though it was mostly because he didn't want Aladdin to see what they thought had happened). When Aladdin revealed himself as the Magi to Sinbad, Ja'far was the first to object about having Aladdin help them stop the Fog Troupe. It can also be hinted that Aladdin would refer to him as Big Brother Ja'far.
- Ja'far (جعفر, Ja'far) means Stream in Arabic.
- He is named after Ja'far ibn Yahya, Grand Vizier of Caliph Harun al-Rashid from One Thousand and One Nights, who in turn was based on a historical figure.
- His special skill is assassination techniques.
- His hobby is work.
- His favorite drink is coffee and he doesn't like alcohol.
- His favorite type of woman is one who contributes to Sindria and he dislikes attendants with no loyalty.
- In his free time, he thinks about what to do for work the next day.
- He is worried about people telling him that he is a bad drunk, since he does not remember anything afterwards.
- His weakness is that he gets mad easily.
- He has learned to work automatically so he can do it even while unconscious. Lack of sleep makes him a bit strange.
- Ja'far works so much that he has no interest in love. However, it seems he has a lot of hidden fans who like seeing him so passionate about work.
- Ja'far was one of Sinbad's first subordinates.
- Ja'far usually only wears official clothing as he only has one set of normal clothing, which he received from Sinbad when he was 14 years old and which no longer fits.
- During his misbegotten youth he used to say things like: "My heart has been frozen since long ago."
- According to Morgiana, Ja'far has no scent.
- Ja'far's favorite type of dishes are elaborate ones he can teach to Sindria's cooks.
- He gets sunburnt easily.
- Ja'far is interested in Kou's Emperor, Koutoku Ren.
- Ja'far's most important property is Sindria's attire.
- Ja'far seems to have a weak spot for children, shown when he worries for Aladdin and after he leaves Kikirku alone, he goes back to apologize to the child after he hears him cry and even saves him from a monster.
- It has been stated in the Magi Official Character Guide Book that Ja'far loves the kingdom of Sindria and Sinbad more than anyone else.
- Though his eyes are black in the anime, in the OVA, his eyes are green.
- When asked who he wished was his real sibling, Ja'far says Masrur and adds: "I don't know why, but please act like one for me." Masrur replies: "Ja'far, please, it's because if things turned ugly, everything will be fine with me nearby."