Eren was the main character of Attack the titans, playing the role of hero at the beginning of the manga and main antagonist at the end. Therefore, many of the things he did had a great impact on the story that would not have happened if he were not in it.
Although other characters, such as Reiner, Historia, and Mikasa, played a bigger role than him during certain parts of the manga, Eren was responsible for triggering events that no one else could have caused. There is no doubt that Eren has made his mark on the universe of Attack on Titan .
10 prevented the Titans from entering Trost
After Eren graduated from the 104th Cadet Corps, he and his companions found themselves on Trost. There, the Colossal Titan appeared and allowed other Titans to enter its interior, forcing Eren to fight his first battle against them. During combat, he discovered his Titan powers, which he used to pick up a rock and carry it to the hole the Colossal Titan had made. That prevented more Titans from entering it. If he hadn’t, the Elders would have lost more land to their predators.
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9 defeated the titan woman
The first Shifting Titan the Study Corps fought against was the female Titan Annie. For years, Eren considered Annie a friend of his as they trained each other. However, when he found out who she really was, he and Mikasa fought Annie. However, before she could be killed, imprisoned, or tortured, Annie formed a crystal around her body, which would not break for years. Luckily, this made it not a threat to anyone for a long time.
8 He was responsible for the death of many of his companions
Although Eren helped the Study Corps achieve many achievements, he was also partially responsible for the deaths of many soldiers. For example, when she fought the Female Titan, she decided to trust her squad members to defeat her rather than help them in the fight. That was a decision that led to their deaths.
Many people also sacrificed themselves to rescue him, such as when he was captured by Reiner and Bertholdt. Although he became the hope of mankind, most of the Survey Corps members who believed in him ended up dying.
7 defeated the Colossal Titan
From the beginning of the series, the Colossal Titan seemed to be the biggest threat Eren would have to face. In the Return to Shiganshina arc, he and Armin teamed up to defeat Bertholdt. Armin devised a plan that led to him nearly being burned to death as Eren sneaked up behind him and defeated Bertholdt. Luckily, Levi injected Armin with the titan serum and fed Bertholdt, turning Armin into a titan shifter.
6 He allowed the Elders to know the truth of the world
Before going to Paradis, Grisha lived in Marley, which allowed her to learn more about the world than any of the Elders in Paradis. After starting a new life, he wrote the truth of the world in his basement, which was forbidden to everyone, including his family. However, early in the series, Eren obtained the key to the basement. When he returned home, with Mikasa, Hange, and Levi by his side, he learned of his father’s past and that his real enemies were people from all over the world, especially the Marleyans. The people of Paradis were surprised to learn of this, but it explained many questions they had.
5 invaded Marley
Like the friends he felt had betrayed him, Eren turned into a monster that killed hundreds of people on purpose. He snuck into Marley and met up with Zeke, who had betrayed his country and started helping the Corps of Inspectors.
When they were ready to return to Paradis, Eren instructed the Inspection Corps to go to Marley and fight their enemies. This showed the entire world how dangerous Eren was. Even the Inspection Corps understood that they could no longer trust the boy who had given them hope.
4 overthrew the military of Paradis
For years, Eren secretly formed his own organization, the Yeagerists, who overthrew the Topography Corps, the Garrison, and the Military Police upon his return to Paradis. They treated their former comrades terribly and hurt those in positions of power within the old army, such as Keith and Hange. Once Eren started the Rumbling, they did their best to stop those who were trying to save the world, including his former friends. Years later, they were still in power, changing Paradis long after Eren’s death.
3 He told Grisha to inherit the Founding Titan
For years, Grisha had planned to steal the Founding Titan from the Reiss family. When the warriors attacked Shiganshina, he thought he was ready to do so, but hesitated. Through the coordinate, Eren was able to go back in time to that moment and convince Grisha to inherit the Founding Titan and kill the Reiss family. Grisha would then pass her two Titans on to young Eren. This created an endless time loop in which Eren was responsible for many of the conflicts that he faced throughout his life without knowing it.
2 He started the rumble
Another way Eren changed the world by being in the coordinate was when he convinced Ymir Fritz to assist him in the Rumbling, the greatest attack humanity had ever faced. Eren disarmed all the Colossal Titans within the walls of Paradis and used them to crush thousands of people to death. This also caused the Study Corps and Warrior Unit to put aside their differences to fight Eren.
1 Helped cause the temporary extinction of the Titans
In the final battle against Eren and his loved ones, Mikasa entered her titan and beheaded him. As he did so, he kissed him, showing Ymir Fritz that he could love someone without blindly taking his side. For centuries, Ymir Fritz allowed the Titans to exist because of his love for King Fritz, but after seeing that Mikasa loved Eren despite fighting him, Ymir got rid of all the Titans. Although the Eldians of Paradis would continue their war with the rest of the world, they had a brief period of time without the dangers of the Titans until the giants finally returned.