Modeler Morpheus

Modeler Morpheus (造形者・モルペウス Zōkeisha Morupeusu?) is the fourth of the sons of Hypnos, the one in charge of controlling the dreams of heroes and monarchs. He is the one that held Tenma captive in the dream world, trapping the Pegasus Saint in a dream-like reality. Morpheus uses the Poppies of the Dream World (夢界の芥子 Mukai no keshi?) to enter the conscience, dreams and hopes of the Pegasus Saint, which are gradually being forgotten as the poppies turn colorless. In the anime adaptation, the technique is renamed Morphium Coma (モルフィウム・コーマ Morufiumu Kōma?).

After Athena's intervention, Tenma frees himself from the poppies, the he briefly fought Morpheus and imprisoned him again, only to be slain for good as Tenma reached the Big Will for a split second, temporarily awakening the Pegasus God Cloth in the process. (source: Wikipedia)