Hecate

Here's my version of Hecate (or Hekate), perhaps one of the most complex and esoteric Greek goddesses ! Originally associated with the new moon (symbol of death and rebirth), childbirth, night and the dead, she later became a deity of crossroads, and more generally of the borders between our world and...the other side. Dogs, as guardian animals, were often depicted surrounding her, and were sacrified to her on crossroads.
Hecate owns the keys of the Underworld, and when Persephone was kidnapped by Hades, she guided her mother Demeter with her torch, and helped Hades' future wife to get used to the world of the dead. She was often represented with three human heads, and at the end of Antiquity, especially after the rise of Christianism, animal heads were given to her, often a dog's and a mare's. She also became strongly associated with witchcraft and ghosts, and is still a popular goddess in modern neopaganism.