Lord Umbria

Morphius is the middle one of the Three, who conspire to keep the dead Praecor Loth in the dark about his own death.

Lord Umbria was a noble and mage at the court of Praecor Loth, who had grown very close friends with the king. Actually, Umbria was a real arrogant man who thought of the superiory of nobles over the common folk. Over time, his whole world revolved around being there for Loth. So when Praecor Loth died, he, like Lethe and Morphius had became literally addicted to his king. He couldn't imagine existing without him, so the he turned all three of them into Liches and they held the soul of their dead king on the world, egoistically serving their need to have him around and denying everyone else their peace.

He didn't see anyone for 700 years, until the Avatar manged to overcome Morphius in Ultima Underworld II. Lord Umbria was impressed at this feat and even recognised Britannia, when the Avatar mentioned it. However, he still thought of him/her as an agent of the Guardian and also revealed himself as still being a very arrogant aristocrat, dismissing Helena's doubts as baseless. So the Avatar challenged him to a duel.

The Avatar slew him and his essence was destroyed for all time. Ironically his egoism in the end prevented him from being with his king in the afterlife.

Trivia

 * Unlike with Morphius and Lethe, Lord Umbria isn't affected by slowly rotting away. Proof that the Liche transformation only works well on mages. Also, Umbria is the most clear-headed of the Three.
 * Umbria recagnising Britannia creates two possible errors. First: If he really only remembers the First Age of Darkness (after all he didn't mantion Exodus or Minax becoming a master of her own), than "Britannia" shouldn't have told him a thing, it should have been "Sosaria". Second: If he indeed does know about Britannia (meaning of after Exodus), then why not mention anything beyond Mondain?
 * That aside, Lord Umbria remembering Mondain makes it clear that the Guardian already existed during Ultima I, which clearly proves the Guardian's origin in Ultima IX wrong.