Konahrik. Dragon Priest Masks are affected by the daedric smithing perk and the dragon priests on Solstheim summon daedra, so it's probably safe to assume that they have something to do with daedra. Anyway, Konahrik is attained after a huge and epic quest to defeat all the dragon priests and carry their masks to Bromjunaar Sanctuary outside Labyrinthian. There you don a wooden dragon priest mask and travel back in time to the ruin's hayday. You place all of the masks in the shrine and the dragon bust opens, revealing the ancient dragon priest mask Konahrik.
This mask will call forth the spirit of its owner to aid you in battle. It's a demon possessed mask with tusks and no mouth people! What's not to like?