Appears in one medieval legend as the offspring of Julius Caesar and Morgan le Fay. Better known as the king of Fairy, particularly in Shakespeare's A Midsummer Night's Dream, where he is at war with his wife Titiana over a question of who has more power.* With the help of his servant Puck, he accidentally casts a spell on his wife, making her fall in love with Nick Bottom, who is now in the form of an ass. But all is resolved, and I think you should really go and read the play.

*This motif shows up in the Irish Tain Bo Cuailnge , where Queen Medb and her husband King Ailill fight over who is more powerful, thus provoking a war. Medb is the origin of Queen Mab in later fairy lore, and Oberon is said in some sources to be the husband of Mab.