Yezidi

The Yezidi were an ethnic group who some European accounts held to worship Satan in some sense. Allegedly this took the form of veneration of the Peacock Angel as a heroic war leader rebelling against a cruel demiurge. There was an inner cult among them who did, in fact, worship a traditionally evil form of this symbol, the Order of the White Peacock. (PROSE: The Book of the War)

Behind the scenes
While the Yezidi, or Yazidi do worship a divinity in the form of a peacock, it's not the case that this is identifiable with Abrahamic notions of Satan - such as the idea of a war leader rebelling. The general association of the two comes from an Islamic parable about Iblis refusing to kneel to Adam, which is seen as an act of hubris and defiance. The Yazidi religion has their peacock divinity also refusing to bow to the first man, but doing so after previously being instructed to bow to nobody but God, so it's seen as an act of piety and passing a test. The similarity of these two stories has led to the Yazidi being persecuted by Muslims who have interpreted them as worshipping their account of Satan.