Eren is the main character of Attack on Titan, one of the most popular anime ever made. When he was first introduced, he was a child who wanted to join the Survey Corps, a branch of the military that fights humanity's predators, the titans. After they broke into his home and one of them ate his mother, Eren joined the 104th Cadet Corps and trained alongside his new comrades.
After they graduated, Eren discovered that he could transform into a titan and became the Survey Corps' greatest weapon. Another soldier from the 104th Cadet Corps, Annie, also had this ability but used it to attack the Survey Corps, leaving Eren to have to fight her at the end of the first season. He's changed a lot since then and here are some of the clearest things that prove it.
Updated March 9, 2023 by Ritwik Mitra: Attack on Titan is a series that has gone through several twists and turns since its inception, with the plot revolving around man-eating monsters before spiraling into tales of political intrigue and the wasteful nature of war as a whole. The show itself is a dynamic spectacle that deals with several mature elements, executing them in a truly impressive manner and proving why the show deserves all its plaudits and more.
The most entertaining part of Attack of Titan without a shadow of a doubt has been the protagonist Eren Jaeger himself. The character has wasted no time in showing just how much of an enigma he really is transforming by leaps and bounds ever since the advent of the first season. Here are some of the most notable and impressive ways he's changed from the young angry man viewers were familiar with in Season 1.
17 He Acquired The Powers Of The Founding Titan
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Eren acquired the powers of several Titans after devouring them, but the manner in which he got the powers of the Founding Titan was something else. After being brought over to the Paths, Eren decided to betray his brother Zeke and appealed to the individual within Ymir, removing her shackles to the royal family in the process.
He reasoned with her and commented on how lonely she must've been all these years, prompting an emotional reaction from Ymir who decided to help Eren out in his genocidal quest. It was a powerful moment with Eren turning into the nightmarish Founder Titan and unleashing a wave of Colossal Titans to destroy the entire world.
16 Anger Stopped Being His Only Motivation
There was a time when Eren simply couldn't control his anger, which is understandable given the trauma he went through as a child. The brutal loss of his mother unlocked a well of anger within him that he accessed to fuel his motivations, from joining the Survey Corps to using the powers of the Attack Titan to bolster humanity's war against the titans that sought to eat them.
However, over time, Eren calmed down and realized how messed up the world really was. His anger at the world diminished after realizing just how fabricated and unnecessary these conflicts really were, causing him to develop some twisted ideologies that ultimately led to him becoming the series' main villain.
15 He Gained An Understanding Of Both Sides Of The Conflict
After realizing that humanity was actually in a conflict against each other, with the Titans being nothing more than byproducts of this aggression, Eren's mind was warped, and he had a lot of thinking to do. Thinking that everyone across the sea was his villain, Eren decided to live amongst the Marleyans in secrecy and figure out what drove this hatred.
This led to him realizing that there was nothing inherently bad or good about either the Marleyans or Eldians. Both groups had been pushed to the brink because of acts carried out in the past, even though they were essentially the same people. It's this realization that led to Eren calming down... although it did lead to another warped thought entering his mind that ultimately led to Eren justifying the very act of destroying the entire world!
14 He Killed A Titan Without Transforming Into One
Eren has killed more than anyone else in the franchise, but he has mostly used his titan abilities to fight his enemies. Because of that, it wasn't until the second season that he would kill a titan the way he was trained to in the 104th Cadet Corps.
When Historia, Ymir, Reiner, Bertholdt, and Connie were surrounded by a group of titans, the Survey Corps saved them. Eren successfully stabbed one of the titans in the neck and was happy to get his first kill that way.
13 He Learned To Accept Reality
Eren couldn't believe it when Reiner and Bertholdt revealed themselves to be the Armored and Colossal Titans. He didn't want to think that someone he looked up to like a brother, as well as another close comrade, could be his enemies. However, once they transformed, Eren knew that he couldn't deny it and fight back.
When Annie turned out to be the Female Titan, Eren hesitated to fight her even though the two weren't close. Being able to fight against two of his close friends proved that Eren learned from his past mistake.
12 He Activated The Coordinate
At the end of the second season, Eren found the titan that ate his mother. When he punched the titan, he activated the coordinate, causing her to be attacked by the other titans around them. At the time, Eren didn't know what this ability was and everyone was surprised that he was able to do this.
It turned out that since Eren inherited the Founding Titan, he could control all the titans whenever he was made contact with someone from the Fritz family. The titan that ate Carla turned out to be Dina Fritz, a distant relative of Paradis' royal family.
11 He Found Out How He Became A Titan
The method by which Eren obtained his powers remained a mystery for a long time. When he met Rod Reiss, the king of Paradis, he learned what happened. His father, Grisha, attacked the Fritz family in order to take Frieda Reiss' Founding Titan. He killed her and everyone around them, except for Rod.
Grisha then injected Eren with titan serum and had his son eat him, giving him both the Founding and Attack Titans that he inherited. Eren wasn't able to remember this, and was shocked that he ate his own father without knowing it.
10 He Learned About Grisha's Past
When Eren remembered that his instructor, Keith, was friends with Grisha, he asked the former commander what he knew about his father. Keith had found Grisha outside the walls. Grisha told him that he couldn't remember much about his past, so Keith brought him to Shiganshina, where he became the district's doctor and met Carla.
However, Eren would learn later on that Grisha's amnesia was a lie. He pretended to forget everything because he was from Marley. With his first wife, Dina Fritz, he led the Eldian Restorationists. Once they were discovered, the group was turned into titans and sent to Paradis. A Marleyan officer that worked with them gave Grisha the Attack Titan and told him to start a new life within the walls.
9 He Went Back Home
When the Survey Corps was ready to retake Wall Maria, Eren was finally able to go back to Shiganshina. It was the first time he, as well as Mikasa and Armin, had been there since they were children and saw the titans break into their home. Once they returned, they had to fight against the Colossal, Armored, and Beast Titans.
Luckily, Eren was able to fix the hole in the wall and was finally able to go into the basement of his childhood home, along with Mikasa, Hange, and Levi. Here, Eren learned about Grisha's life in Marley, along with other secrets about the world beyond the walls.
8 He Defeated The Colossal Titan
Since the first episode, the Colossal Titan seemed to be the biggest threat in the series. Without Bertholdt kicking down the wall and letting the titans into Shiganshina, a lot of the events in the series wouldn't have happened. During the Survey Corps fight against the Colossal, Beast, and Armored Titans, Eren and Armin teamed up to defeat Bertholdt.
They were able to trick him into letting his guard down and defeated him. However, as a result, Armin was almost burned to death. In order to save him, Levi injected Armin with titan serum and had him eat Bertholdt so he could inherit the Colossal Titan.
7 He Saw The Sea
When they were kids, Armin showed Eren a book that he found. By reading this book, they learned that other places around the world were very different than the island they lived on. The place that Armin wanted to go to the most was the sea, which Eren didn't think was real.
At the end of the third season, the two of them, along with their friends, went further away from the walls than they ever had before and eventually reached the sea. After all these years, one of his goals came true, but instead of being happy like Armin and the others were, he thought about killing their enemies on the other side of the sea, hoping that doing so would give him the freedom he always wanted.
6 He Went To Marley
The beginning of season four takes place a few years after the Survey Corps went to the edge of Paradis. Eren finally went to Marley and pretended to be injured, so he could spy on his enemies at a hospital. Due to the time jump and how much more he learned about the world, Eren's personality greatly changed.
This new side of Eren was nothing like what fans would have expected him to become. He attacked Marley the same way Reiner and Bertholdt attacked Paradis, he manipulated a young warrior named Falco into sending a letter telling the Survey Corps to join him, and he killed a bunch of innocent people so he could inherit the War Hammer Titan before going back home.
5 He Betrayed The Survey Corps
Out of all of Eren's actions, betraying the Survey Corps was the most surprising. After having them help him fight the warriors in Marley, he and Zeke, the inheritor of the Beast Titan who was also Grisha's first son, returned to Paradis. Because of his actions, Eren lost the Survey Corps' trust.
However, Eren had planned this for a long time and secretly turned some of Paradis' soldiers, as well as many civilians, onto his side. He led a revolution and overthrew the military. The titan shifter that gave the Survey Corps hope became the Eldian devil that took their hope away.
4 He's Made His Peace With Killing Innocent Civilians
There was a time when Eren was torn at the idea of killing fellow humans. After all, the battles he was waging were against other Titans, so to suddenly kill other humans during the Royal Government arc was a tough pill to swallow for him.
However, after the time skip, it seems that Eren has no problem with killing humans at all. The vicious manner in which he destroys Marley and kills a whole host of innocent citizens is downright terrifying to witness.
3 He Broke His Bonds Of Friendship With Mikasa And Armin
While the betrayal of the Survey Corps was already surprising enough as is, Eren's betrayal of the Survey Corps was made even worse when he went so far as to break his long-lasting friendship with Mikasa and Armin as well.
The chilling manner in which he berates Mikasa is absolutely horrific to witness, forcing Armin into a rage as he punched his once-best friend. It seems that Eren has gone past the point of no return and has permanently severed any and all bonds he had.
2 He's Fine With Committing Genocide For The "Greater Good"
There was a time when Eren cared mostly about minimizing as many losses as possible. However, over time, it seems that Eren has come to accept the idea of having to finish off the Subjects of Ymir to finally end the cycle of hatred once and for all.
What this basically means is that the Eldians would euthanize their entire race in a bid to leave no one around who can take on the power of the Titans. It's an extreme plan that certainly has its holes... but, as per Armin, it's also an extremely noble act as well.
1 His Hairstyle Is An Obvious Yet Notable Change
While this point might be a bit moot, talking about Eren's hairstyle is quite important. After all, most Japanese media tend to keep a character's haircut in high regard, with their entire character changing if they ever wish to don a different look.
This is precisely the case with Eren. A naive boy who used to have the most ordinary hairstyle decided to take an extreme step to destroy the cycle of hatred, losing his innocence in the process. This is reflected by his change in his personal appearance.