Revenants are dead Named, that the Dead King has necromanced up to serve him.
there are at least 50+ of them, which the group saw when walking to Neshamahs hall. a honor guard cat or archer called it.
When turning Named into Revenants, the Dead King can cull the aspects to his choosing, or let the Revenant keep their memories, such as the Good King was done to, as punishment or a cruel joke. ( dont quote me on this , i might be lying )