The Mordred answer is a great one. To add a new name to the list though, I'll pick the Korrigan. Old stories of them would eventually inspire Tolkien to write The Lay of Aotrou and Itroun, which is a delightful read about a couple that wants to have a child but struggles to conceive. The noble husband encounters a strange woman in the woods that offers to help, fuckery ensues.

Edit to add, just in case that doesn't scratch your mythology itch the right way, another great one: Set or Seth from the Egyptian pantheon

Another edit because I can't help myself: Enlil! He's from the Sumerian mythos, and in the Atrahasis story he is the god that decides to send a flood to wipe out humanity. Luckily, another god named Enki has a human he really likes that he gives a head's up to. Another fun story that shares some similarities with the Noah's Ark story.