The past is the past, but there is always the future.
Sensei Wu is a main character in LEGO Ninjago: Masters of Spinjitzu and The LEGO Ninjago Movie. He is a wise old man and the mentor and master to the six Ninja (Lloyd, Kai, Jay, Cole, Zane, and Nya). He is the First Spinjitzu Master's second born son, Misako's brother-in-law, Garmadon's younger brother, and Lloyd's paternal uncle.
Despite his advanced age, Wu as the ninja master is still fit and can hardly be beaten. Before he taught the current ninja, he fought with his brother and elemental armies against the evil in Ninjago, sometimes in the serpentine war or against the masters of time. But Sensei Wu was already had a disciple before his current one: Morro, the master of the wind. The old man had helped him master his strength after finding him neglected by the containers of the monastery, where Morro and a few of his friends had been looking for food. He also always had special feelings for Misako.
Many years later, after bringing the four Ninja together, he taught them the art of Spinjitzu and the handling of the four golden weapons. However, shortly thereafter this monastery was burnt down by the serpentine and since then the Ninja have been trained and trained mostly on a modified ship, the Destiny's Bounty. The Master has been assisting the Ninja throught their many conflicts and adventures.
In a fight with Acronix, however, he was hit by the Advance Timing Blade and aged very fast. Although he could be rescued before the end of the seventh season, he sacrificed himself and disappeared with Acronix and Krux in the time vortex. The ninja, nearly devastated, then appointed Lloyd to be their premature master; because their goal was to find Master Wu; no matter what happens.
Wu continued to battle the Time Twins and was presumably able to defeat them before he somehow exited the vortex. However, the time blades' affects had caused him to regress into that of a toddler. Fortunately, Misako was able to track him down and he's been back ever since, even if only as a toddler. He is also the brother of the cruel Lord Garmadon, both sons of the first Spinjitzu master. His nephew is Lloyd Garmadon, who turned out to surprise everyone as the legendary Green Ninja. He usually wears the staff of the first Spinjitzu master as a weapon. He is in love with Misako, but she chose Garmadon because he intercepted his love letter and replaced Wu's name with his own .... but despite that, Wu and Misako have come closer since the second season. His spinjitzu has a golden color, which corresponds to the power of creation inherited from his father.
At first Wu had shown, according to Kai, to be a senile and crazy old man, but over time he has proved to be a great Ninja who is always willing to protect others. At first he thought that his ninja students needed more discipline and that they not only think about physics but also think about things. Almost always calm, and without showing anger.
Sensei Wu, Nya, Dr. Julien & Misako
Wu talking with Nya with Misako & Zane's Falcon
Sensei Wu saved Garmadon's life
Pythor is changed Sensei Wu to evil
Kai, Nya and Wu face the Time Twins in the Iron Doom.