Benedict Cumberbatch as Hypnos, God of Sleep. Hypsnos was Nix and Erebus 's son. His wife, Pasithea, was one of the youngest of the Graces and was promised to him by Hera, who is the goddess of marriage and birth. Pasithea is the deity of hallucination or relaxation. Hypnos lived next to his twin brother, Thanatos in the Underworld. He is said to be a calm and gentle God, as he helps humans in need and, due to their sleep, owns half of their lives.
Benedict has a genetic mutation called Sectoral Heterochromia Iridum. What this means is that the pigment found within the iris, called melanin, is unevenly distributed, and causes a distortion in the colors. Blue eyes have a very low level of melanin, while green eyes have a higher amount. When inherited, the mutation is harmless - it does not affect the vision or weaken the iris muscle in any way, just gives it a very mystical, rainbow-like effect.