Erwin Smith named Hange Zoë the 14th commander (Danch?) of the Survey Corps before his death. Hange was previously a squad leader in charge of the Fourth Squad, in charge of developing and conducting research on Titans such as Eren Yeager.
After being elevated to the commander, Hange was in charge of expedition planning, regimental management, recruiting, and all of Erwin’s previous responsibilities. Armin Arlert succeeded them after they died.