In Norse mythology’s Ragnarok, Odin leads the Einherjar from Valhalla into battle. The Einherjar are warriors chosen from the slain and gathered by the valkyries for an anticipated final conflict.
Valhalla is Odin’s hall in Asgard, where the chosen dead feast and fight repeatedly as preparation. At Ragnarok, this training reaches its climactic purpose: the warriors leave the hall to fight alongside the gods. Odin’s command reflects his role as a war god, ruler, and seeker of knowledge about fate.
This question differs from asking who commands Valhalla in general. Odin owns and rules the hall, while the valkyries select and escort many of the dead there. The Einherjar are not all fallen warriors from every battle; they are the specially chosen dead associated with Odin’s hall.
Odin’s participation ends tragically. Fenrir kills him during the battle, after which Vidar avenges his father by killing the wolf.