Sensei Wu, also known as Master Wu, is a Spinjitzu Master and mentor of the ninja team from Ninjago City. It's kinda rare you see modern ninjas, but beggars can't be choosers.
Oh, and he turned bad because of a Nindroid thing or whatever. Either that or Pythor. But Pythor is too laid-back for that sort of thing, anyways.
The good sensei defeated Craniac, Brainiac, and Kit Fisto, but lost to Dr. Inferno in the next match. In Round 2, Invizable, Flintlocke, and Metalbeard met their match at the hands of Sensei Wu, but he was once again defeated by Dr. Inferno in the runoff. Note to self: Scientists and Spinjitzu teachers do not mix.
Season 3: NexoByte