There are many Reasons which makes him one of the best anime character

Eren Yeager was a former member of the Survey Corps.

Eren swears revenge on creatures known as Titans that devoured his mother and destroyed his town. 

In order to defeat the Titans, Eren enlists in the Military and joins the Survey Corps 

Eren gains the power of becoming a Titan later identified as "Attack Titan" 

He was the main protagonist of Attack on Titan

Eren possessed the power of 3 Titans. From his father, Eren inherited the Attack and Founding Titans. After eating Lara Tybur during the Raid on Liberio, he gained the War Hammer Titan as well. 

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