When Attack on Titan first began, Eren Yeager was the main protagonist of the series. However, over the years, he became an antagonist, being the final enemy that many other main characters—including his friends—would fight against.
Though it seemed shocking that Eren would go down this dark path when fans saw him kill thousands of people and betray those that cared about him the most, it makes a lot of sense looking back on it. There were signs all the way back to when he was introduced, foreshadowing who he would become by the time the manga ended.
10 He Always Wanted To Kill His Enemies
Eren wasn't like most children. He was always willing to kill those that he felt took away his freedom, without giving it a second thought.
Though this was a good thing at times, such as when he saved Mikasa by killing the human traffickers that kidnapped her and murdered her parents, it's also very concerning for a child to be so aggressive at such a young age. Things got even worse once the Titans broke into his home, as he swore that he would kill all of them.
9 He Ignored Those That Wanted Him To Live A Peaceful Life
Those that knew Eren when he was a child, such as Mikasa, Carla, and Hannes, were concerned that he would go down a dark path and tried to stop him. Mikasa tried to convince him not to join the military, and only joined with him so she could make sure he'd be alright. One of the ways that Mikasa tried to stop him was by telling Carla, who was against the idea.
Hannes, on the other hand, always felt like Eren could become a great soldier since he always stood back up after being knocked down, but even he didn't think it was a good idea for Eren to join the military. No matter what any of these characters did though, Eren never listened, walking away from the quiet and peaceful life they wanted him to have.
8 He Became A Titan Shifter When Titans Seemed To Be The Main Antagonists
At the beginning of the series, the Titans seemed to be humanity's greatest threat. Neither the Eldians inside of Paradis nor the readers had any idea that there were humans that wanted to kill them outside of the walls, or that some people had the ability to transform into a Titan.
Eren seemed to be the first person that was given this ability, turning him into an even greater threat than the normal Titans. Some people around him even feared his powers and wanted him to be executed, knowing that he could one day start an attack on humanity.
7 He Learned A Lot From Annie & Reiner
After Eren, Annie and Reiner were two of the people that were revealed to be Titan Shifters at the beginning of the series. Eren learned a lot from both of them when they were all soldiers in the 104th Cadet Corps.
One day, Reiner and Eren had to fight against each other during training, in case if they ever needed to fight against another human. After Eren knocked Reiner down, Reiner told him to be the bad guy next time. He may have taken that a bit too literally.
6 He Tried To Hurt Mikasa When He Transformed Into A Titan
After Eren's powers were discovered, the military tried to get him to cover a hole with a boulder to stop Titans from getting into Trost. Though Eren was able to do this, he lost control of his Titan at first, and tried to hurt Mikasa.
She tried to snap him out of it as the soldiers around them began to lose faith in Eren. Luckily, he came back to his senses and saved the day, but the military wouldn't be able to control him forever.
5 Levi Knew That He Was A Monster When They First Met
Even though Levi saw a lot of potential in Eren, he also knew that he always needed to keep an eye on him. That's why he made sure that Eren joined his squad and that the other soldiers in it would be strong enough to both protect Eren and take him down, depending on what Levi needed them to do.
Levi even told them as they tried to escape from the Female Titan that Eren was a monster, even if he didn't have Titan powers, because he would never submit.
4 Grisha Killed The Reiss Family In Order To Inherit The Founding Titan
Eren didn't know how he became a Titan Shifter at first. However, after Rod Reiss captured Eren and Historia, he showed the two of them how it happened.
The Reiss family had inherited the Founding Titan for generations, until Eren's father, Grisha, killed most of them and took the Founding Titan for himself, before passing it down to his son. The way that Eren became a Titan Shifter was terrible, resulting in the deaths of members of the royal family, most of which were children.
3 He Told Levi That Armin Would Save Humanity Instead Of Him
When Armin was nearly burned to death by sacrificing himself in order to defeat Bertholdt, and that Erwin almost died after being hit by debris that Zeke threw at him, Levi had to choose which one to save.
Because Armin was there for Eren since they were kids, Eren begged Levi to save Armin, telling him that neither Erwin nor himself had what it took to save humanity. This would eventually turn out to be true, as Eren became a sinner rather than a savior.
2 Zeke Turned Out To Be His Brother
When Zeke was introduced, many thought of him as the greatest antagonist at that point in the series. He proved to be stronger than Reiner, took more action than Bertholdt, turned the villagers of Ragako into Titans, and killed the majority of the Survey Corps.
Nobody would have ever expected him to be Eren's brother, but he turned out to be Grisha's first son. Though it may not have been Grisha's intentions, he had a role to play in how both of them became antagonists.
1 He Thought About Killing People On The Other Side Of The Sea
For years, Eren wondered what was in the basement of his childhood home. Grisha even left him the key there so he could find out after he turned Eren into a Titan Shifter. When Eren, along with Mikasa, Levi, and Hange, returned there, they found out that Paradis was just a small island compared to the rest of the world, where not only did humans live, but wanted the Eldians inside of the walls to die.
Eren didn't get freedom, even after he went to the ocean like he and Armin wanted to do since they were kids. Instead, he thought of what would happen if the people that wanted him and his friends to die perished instead.