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Amar is first mentioned in Allegiant as the instructor who trained Tobias, giving him the nickname of Four when he found out Tobias only had four fears. Tobias told Tris Prior that Amar was dead because he was discovered as a Divergent and subsequently killed by Dauntless and Erudite.
Amar is introduced after Tobias has gone through his Choosing Day ceremony, and transferred to Dauntless from Abnegation. When Amar refers to Tobias as a 'Stiff,' an Abnegation reference, asking Tobias what his name is, Tobias tells Amar he can call him Stiff, for all he cares, not wanting to be known as the son of Marcus Eaton. Amar introduces himself as their instructor, and reveals they'll be going through their fear landscape on their first day. When Tobias goes through, Amar finds out about Marcus and the abuse Tobias endured, but is impressed when finds out Tobias has only four fears. Amar realized Tobias was trying to escape his past, and gave him the nickname "Four" to help him. Tobias accepted it, marking the start of his Dauntless initiation.
Tobias mentions that Amar was the one who taught him how to throw knives during his training, reflecting now that he's doing the same thing for the new group of initiates. Later, he says that Eric, his fellow initiate, now a Dauntless leader, started closely watching Amar the year before, noticing his Divergence. Soon after, Amar was pronounced dead when he was 'dead' by the train tracks.
When Tris and Tobias go outside the fence of the city with a group of people, they find Amar alive and the Bureau of Genetic Welfare, where he has been staying. He reveals that Tris' mom, Natalie Prior, helped him fake his death after he was discovered as a Divergent before he was smuggled out of the city. He works in security now, guarding the Bureau on the outside. Initially, Tobias is in shock and anger at Amar's duplicity and lies, but later understands he was trying to do what he could to survive. Amar is visibly relieved when Tobias shows he's no longer angry with him.
Amar was in a relationship with George Wu.
Tris is offered a place on the Board of the Bureau, and is given the chance to go on a security patrol. She accepts, and joins Amar and George when they go on a reconnaissance mission of the fringe area. Initially, they're set up to get information, but when they're ambushed, Amar goes to help George out when he's cornered. Tris is able to get the fringe to back down while they return to the compound.
On the ride back, Tris asks Amar about Tobias, and he reveals that he was once attracted to Tobias, but when he realized his feelings weren't returned, he backed off. He also reveals he's now in a relationship with George, and asks Tris not to tell anyone because the Bureau would see it as a violation of their rules. Tris tells him she won't tell, not caring about the Bureau's wish for pure genetics. Amar also tells Tris that he was worried because he saw Tobias as "obsessive, compulsive, insecure." However, he feels like Tobias is a better person now that he is with Tris, and believes she's good for him.