Armin Arlert is the current commander of the Survey Corps, which was named by Hange Zo before their death. He is also a childhood friend of Eren Yeager and Mikasa Ackerman, as well as one of the series’ two deuteragonists.
Although he looks to be one of the 104th Training Corps’s physically weakest members, his brains and strategic genius make him an important asset, especially when coupled with Hange. After the fight at Shiganshina District, he took the Titans’ power from Bertolt Hoover and obtained the Colossus Titan.