Aether

Twin brother and husband of Hemera, goddess of Day, Aether was the god of air and light.

= Myths = Aether married his sister, Hemera and fathered the girl form of Pontus, Thalassa. He was the first son of Nyx and Erebus. His Roman form is Aether.

= Trivia = Aether and Hemera, Gaia and Tartarus. A brother marrying sister relationship is completely normal in Greek Mythology like Zeus and Hera.