Outwardly, Morpheus is the supreme leader of the Children of the Cathedral. Though he adopts a pious demeanor and can sound a bit like an old-time country preacher, he does not believe that the Holy Flame, the Dark Lord, the Master is, in fact, a god. Morpheus is intelligent, crafty, sly, greasy, and thoroughly evil. Ensnared by the promise of power rather than by belief, he has a short fuse and terrible anger, which makes him an extremely dangerous individual.
Morpheus used to be a member of the Rippers, a gang of inbreds familiar to him, but he eventually left the gang and became the leader of a doomsday cult. In 2151, he was found by the Master's spies and pledged his followers to him, forming the future core of the Children.
Morpheus lives in the Cathedral, on the tower's highest floor. It is here that he oversees the immediate goals of the Children and holds their Communion by means of large, propaganda-esque monitors located on the main floor. He dies in 2162 by the Vault Dweller's hand, either in person or as the Cathedral is destroyed.
Even though Morpheus might seem as a respected character in his community, he is considered only a pawn by his superiors. Especially Lieutenant, the Master's right hand, does not think very highly of him and actually wishes he dies a painful death eventually.
Pestering him causes him to say “You were warned. Guards!” in a float complete with voice acting. He and Nicole are the only two characters in the game where this happens.
He seems to follow the Master blindly, never questioning his superior(s), as can be told from dialogue choices.
It is usually impossible to approach Morpheus normally for conversation because the nearby nightkin automatically turns hostile if you have any companion with you (including Dogmeat), which, by extension, also makes Morpheus hostile. Even with a COC badge and robes, you will be attacked by the nightkin immediately.
Combat can be bypassed if you have a Stealth Boy, a high enough Sneak skill, and a high enough Intelligence, although if you just stand there, another nightkin will move closer and see you.
Lasher can be convinced about needing to see Morpheus. If the Vault Dweller tells Morpheus that Lasher sent him up, there is a skill check. If failed, Morpheus will attack out of suspicion. If passed, Morpheus allows the Vault Dweller to leave and says that Lasher likes to get Children into trouble.