Abal the Defiler, (a.k.a. The Mummy King), is an enemy found at King's Rest in Alik'r Desert. To reach his location the Vestige needs to travel through Motalion Necropolis, then ride down to the beach where he will be ready and waiting for their arrival.
He will be doing the ritual motion to the dead kings corpse. When engaged in combat the corpse will rise from the gave to fight alongside Abal The Defiler. Abal will summon zombies as well as root you to the earth. The Vestige will need to either stun him or break from the roots. The King will do melee damage to them as well as vanish for sneak attacks while they are down. The dead king is not hard to handle when Abal is dead and unable to root them down.