During the reign of the Second Hokage, he was one of the ANBU ordered to watch the Uchiha clan to keep them from rebelling again. Baku is likely not his real name, but a codename.
Peeking from behind his mask, his eyes were said to be able to perceive everything.Baku had fire release as he could perform many fire release jutsu he specialised in assasination. he was a respected senpai in the anbu. he was a jonin level anbu. he had completed 921 missions. It is romoured that he was killed by two elite uchiha jonin while he was collecting research he was a jonin so he wasnt defeated easily.
A baku (獏) is also a mythological Japanese creature said to eat dreams and nightmares. As a chimera with an elephant's trunk, a rhinoceros' eyes, an ox's tail, and a tiger's paws, they resembled somewhat the real-life tapir. After the two creatures were connected, the Baku was more and more often depicted as a tapir. Modern images depicting Baku as actual chimera are rare.