Eren Jaeger (エレン・イェーガー Eren Yēgā) is a member of the Scout Regiment and the main protagonist of Attack on Titan. He is the only son of Grisha and Carla Jaeger, the adoptive brother of Mikasa Ackerman, the younger paternal half brother of Zeke Jaeger and the holder of the Attack Titan and the Founding Titan.
After waking up from a nightmare interrupted by Mikasa, they stroll through the city and Eren expresses anger at being kept like cattle within the Walls, revealing his intentions in joining the Scout Regiment. Mikasa scolds him, not taking his words seriously, and later reveals what he said to their parents.
Carla is shocked and angered, saying she will not let him join the Scouts due to their high mortality rate. She begs Grisha to talk some sense into Eren, but Grisha ignores her objections and instead announces that he will be leaving for a few days on a trip and that when he comes back, he will show Eren what he has hidden in the basement of their home. Enthralled, Eren joins his mother and Mikasa in waving him off. Carla reminds him that she will not allow him to join the Scout Regiment, and they exchange a heated argument before he runs off.
Eren and Mikasa scare off bullies harassing their neighborhood friend Armin Arlelt. Eren offers Armin a hand but Armin rejects, expressing discontent with his abilities to protect himself and admits he is weak. The three stroll through Shiganshina and settle by the riverbank, where Eren reveals his intentions of joining the Scout Regiment to Armin.
Suddenly, lightning strikes, and an earthquake breaks out. The three gather in the center of the district with other civilians, where they all gawk in horror at the sight of a Titan larger than Wall Maria. The Titan kicks a hole through Wall Maria’s gate, sending massive pieces of debris throughout the town.
Eren and Mikasa hurry home as Titans begin entering the district, arriving to find their house crushed by a large rock and his mother trapped beneath the rubble. She says that the rubble crushed her legs and she can not move, but Eren insists that he will carry her to safety. As they argue, a Titan begins approaching the collapsed house. A Garrison member, Hannes, arrives and Carla begs that he takes the kids and run. Hannes rushes to kill the Titan and save Carla, but quickly changes his mind and takes Eren and Mikasa away. As Hannes carries the two on his shoulders and retreats, Eren witnesses as the Titan eats his mother.
As the evacuation of Shiganshina is underway, Eren, Mikasa, and Hannes arrive in an alley and Eren starts attacking Hannes with leaving his mother. Hannes says that the reason Eren could not save her was that even though he had the courage, he lacked the strength, and Hannes himself lacked the courage even though he had the strength.
Hannes leaves Eren and Mikasa on the boat leaving the Titan-infested city. There, Eren and Mikasa witness an Armored Titan destroy the back gate of Shiganshina. Eren, Armin, and Mikasa are forced to depart on the boat as Eren realizes that he can never return home, and vows to kill every Titan in existence.
After the fall of Wall Maria, Grisha finds Eren and takes him into a nearby forest. Grisha instructs Eren to retake Wall Maria and gives him the key to the basement, before giving him a Titan injection that turns him into a Pure Titan. Eren instinctively eats his father, granting him the Power of the Titans.