Sensei Wu

Sensei Wu is the youngest son of the First Spinjitzu Master. In Wu's childhood, he and Garmadon were the best of friends. One day in his youth, Wu lost his father's katana during a spar, and Garmadon climbed over the wall to retrieve it. While outside, the Great Devourer bit Garmadon's hand, corrupting him with it's venom. As a result of the growing evil within him, Garmadon became increasingly distant from his family, but he and Wu would remain civil with each other for some time. When Garmadon married Misako and fathered Lloyd, Wu was happy for his brother, but also somewhat melancholy, as he personally harbored some affection for Misako. 

After their father died, Wu and Garmadon vowed to protect the Golden Weapons. Garmadon, however, planned to steal the Golden Weapons, but when he tried, Wu confronted him and they fought. Wu won the battle and banished Garmadon to the Underworld.