Mannimarco is an altmer necromancer, lich, leader/founder of the necromancer’s cult ‘The Order of the Black Worm’, and arch-nemesis of Vanus Galerion and the Mages Guild.
He was born around the second era 210 on an island called Artaeum, the third largest island in the Summerset archipelago. He used necromancy from the start and was confronted beneath the Ceporah Tower by his fellow student and founder of the Mages Guild, Vanus Galerion. Mannimarco ignored his warning and was later sent to Tamriel by his masters either on an undescribed errand or as a rather feeble punishment for his use of the dark arts. He used the opportunity to gain followers and spread the practice of necromancy. He became a lich either as the first in existence or the first human to become one (it’s never specified) which explains his longevity as he’s almost 1,130 years old at the start of the Oblivion Crisis. He was later attacked by Galerion who called him "The Worm King" in a great battle where approximately a thousand men died including Galerion. Many had assumed Mannimarco perished in this battle as well.
After Arch-Mage Traven took a stance against necromancy the Mages Guild lost many members and gained many enemies. Mannimarco used this opportunity to expand his cult and launch an all out attack on the Mages Guild in Cyrodiil. He was present during the destruction of the Bruma Mages Guild, leaving J'skar the only survivor so he could relay what happened.
Mannimarco carries a unique artifact called the Staff of Worms and is associated with two other artifacts called the Necromancer's Amulet (which he himself created) and the Bloodworm Helm, both of which he lost possession of to the Mages Guild.
"I... I saw his face. I saw the King of Worms! I couldn't believe my eyes. I think the only reason I'm alive is because I was invisible... but even so, I think he saw me. He killed them, one by one. Volanaro was last, I think. He was trying to run away, but he didn't make it, did he? The King of Worms stood over him, right before he died, and he... well, it looked like he sucked out Volanaro's soul! He said something about Echo Cave, and destroying the Mages Guild. Then he looked right at me, and grinned!" -J'skar
"I must say, I expected Arch-Mage Traven, rather than his star pupil. I am disappointed to see that he could not face me himself. I have met so many of his predecessors over the years. I developed a particular fondness for Galerion, ill-preserved though he may be. But here you are instead. Skilled enough to make it this far, which speaks volumes about you. Perhaps you'll be as useful to me as Traven would." -Mannimarco (Oblivion)