Oberon is best known from Shakespeare’s Midsummer Night’s Dream, the king of the faeries who interferes with the love lives of mortals, and plays tug-of-war with Titania over trinkets and toys (read: people) they both want. Oberon was most likely taken from a legend of a Merovingian sorcerer named Alberich, or “elf-ruler,” who was believed to be the other-worldly brother of Merowich, whom the people got their name from.
The name Oberon first showed up in a French heroic song, about a fairy who was cursed to a dwarfish height by an offended fairy at his birth (hello, Sleeping Beauty?) but was given great beauty in consolation. In the poem, Oberon aids the hero in winning a pardon for killing the emperor’s son in self-defense, after performing various feats. This poem was based on bits and pieces of fact of a true hero who lived in the ninth century, but was understandably embellished. In it, Oberon had a magical cup, which has been compared to the Holy Grail, which was always full for the virtuous.
In Midsummer Night’s Dream, Oberon wants to a human child that Titania’s taken into her care—it’s the child of a mortal friend of hers who’d died, and she wants to raise it for her friend, but Oberon wants to have the child for his own purposes, to raise as a henchman, basically. To distract her, he uses a magical ointment that he has put into her eyes, so that she falls in love with a man who’s been given a donkey’s head—meanwhile he has his servant Puck meddle with two pairs of lovers that are wandering in the woods, with a mistake or two made along the way. Eventually he feels badly for what he’s done to his Titania, though, and the two are reunited.
Given the title of King of the Faeries, Oberon is understandably mentioned here and there in other works of fiction, of a more contemporary nature. As a few examples, he’s mentioned briefly both in Susanna Clarke’s Jonathan Strange and Mr. Norrell, and also in Frewin Jones’ Faerie Path novels.