So, Apollo is one of those macho gods who always falls in love with some human woman at some point. He falls in love with Coronis, who is pregnant with his child. Being the suspicious god he is, he sends a crow, then pure-white, to watch over her.
Coronis isn’t one of those loyal types, and when she falls in love with someone else, Apollo finds out fast, and boy does he get angry! Angry that the crow didn’t peck out this man’s eyes, he scorches the bird’s feathers black and from then on they represented beings of revenge.