Chernobog

You might have heard this name sometime before, whether because of the game SMITE, or the Disney film Fantasia, all agree that Chernobog is a sinister figure.

In Slavic mythology, Chernobog (alternatively spelt Chernabog or Czernobog) is the "Black God", the god of evil, darkness, and death. He is the twin brother of Belobog, the god of light and goodness, making both brothers balance between good and evil, light and darkness, life and death, etc...

He is a playable character in SMITE, appears as the giant demon at the end of Disney's Fantasia, and is one of the Old Gods recruited by Mr. Wednesday in American Gods (I might make a skin based on his appearance there).