Board Thread:Oblivion/@comment-92.40.51.250-20131201150336/@comment-74.254.158.41-20150620081253

Mannimarco, the King of Worms, can be in both games because of the fact that he's a necromancer. They use the dead for their own benefit and that can include sing them for his own life. Thus, he became a lich and lived on to either the 3rd or 4th era. (Depends on when you did the quest, Oblivion takes place in two eras.) So, he lived for that many years and Bethesda decided he would be a nice reference to the Mages Guild questline in Oblivion without breaking the lore. It all makes sense even without the alternate realities that Morrowind made possible. He could've simply lived a long period of time, as they would have us think without us over-analyzing the situation of his presence in multiple titles.