Raven skull carvings

In Greek mythology, ravens are associated with Apollo, the god of prophecy. They are said to be a symbol of good luck, and were the god's messengers in the mortal world. According to the mythological narration, Apollo sent a white raven, or crow in some versions to spy on his lover, Coronis. Raven is the messenger of the Sun Gods, both Helios and Apollo.
The pagan Danes and Vikings used the raven banner on their ships, in Odin's honor. These flags, usually sewn by the daughters of great warriors and kings, were tokens of luck on their voyages. Houses where ravens nested were also thought to be lucky.
Odin had two ravens - Huginn (thought) and Muninn (memory) who flew about the world, delivering messages, gathering knowledge and reporting back to him. One of Odin's many titles is Hrafna-Gud, the God of the Ravens. Odin's daughters, the warlike Valkyres, were sometimes said to take the shape of ravens.
Raven is also the totem of the pan-Celtic Sorceress/Goddess Morgan le Fay, who was also called the Queen of Faeries.