Within the world of "Critical Role," Vecna was a mortal archmage who achieved lichdom hundreds, if not thousands, of years before the events of Campaign 1. He grew an army of followers and made plans to ascend to godhood through a "Ritual of Seeding," though he was eventually betrayed and killed by his lieutenant, Kas the Bloody-Handed.
Vecna's return to Exandria was first teased in Campaign 1, Arc 1, and is fully achieved in Campaign 1, Arc 5, when the Lady Delilah Briarwood (Mercer) successfully revives Vecna at the Tower of Entropis in the Shadowfell. This occurs in "Critical Role" Episode #103, "Race to the Tower," in which Vox Machina arrives too late and is forced to duel Vecna atop Entropis. What follows is perhaps the worst beatdown Vox Machina suffers in the entire campaign, as Vecna, Briarwood, and their supporters easily hold off Vox Machina and teleport their home base of Thar Amphala to Exandria.
During the battle, Vex Vessar dies at the hands of a "Power Word Kill" spell, Grog Strongjaw is banished back to the Shadowfell, and Vax Vessar is turned to dust by a "Disintegrate" spell. Though Vex is revived by Pike Trickfoot, and Percy manages to kill Delilah Briarwood, the party's first fight with Vecna ends in Vax's death and a "Planeshift" retreat courtesy of Keyleth.
