The Abbot is the winged being (assumed to be a fallen Aasimar) in charge of St. Markovia's Abbey. He believed that if he can create a golem bride for Strahd, Barovia would be saved. The Wafflecrew got the sense that the Abbot was secretly in love with the golem bride. The group brought Diath's corpse to him so that he could resurrect him. He did, because Diath's ghost possessed the corpse bride and convinced him to.
When the group returned to Barovia, Paultin was meant to marry Vasilka. Escher warned Paultin that the Abbot still had good in him. Paultin and the Abbot had an altercation before the wedding.  The group learned that the Abbot had put Ireena's head on Vasilka's body.