Walpurgisnacht

Walpurgisnacht was a witch before Kaname Madoka made a wish to rid the universe from them.

It is heavily implied that Clarisse van Rossum is the Magical Girl that originated her, e.g. in Chapter 22: Shifting Winds Clarisse arrives at Mitakihara on the same place and time that Walpurgisnacht did when witches existed.