Erh Lang, also written as Erh-Lang, Er-lang, and Erlang*, is the Chinese God in charge of chasing away evil spirits. He guards the Jade Emperor's palace, and is a nephew of the Jade Emperor, Yu-huang. When banishing evil spirits he has the help of T'ien-kou, the celestial dog (sometimes one dog, sometimes many, depending on the story). Erh Lang also had the ability to shape-shift.
Shape-shifting tuned out to be Erh Lang's doorway to greatness; he defeated the rampant Monkey King (Wu-k'ung), a task at which all others had failed. The Monkey King had bullied his way into a position of great power, and all the Emperor's men, most of them gods, hadn't been able to do anything about it. Erh Lang and his men attacked en masse, and managed to scare off the Monkey King's army. One of the Monkey King's abilities was changing form, so he and Erh Lang had a battle of shape changing ability, mostly consisting of the Monkey King trying to find a form that could out-distance or hide from Erh Lang. (This 'shape-changing battle' is common in stories of magic users, but these two battled like this through 300 rounds, making this one of the longest fights and most boring stories ever). Eventually the Monkey King did escape, and in time rose again.
Erh Lang is known as the Great Restorer, and the Sustainer. His birthday is August 15th.
* Erlang: it's not only a god, it's also a programing language.