Who is Watanabe from Unbroken: A World War II Story of Survival, Resilience, and Redemption and what is their importance?

Mutsuhiro Watanabe was a Japanese corporal and prison guard during World War II. He was especially brutal to the prisoners in his charge, particularly with officers. He had a reputation for constantly changing the rules of behavior, then punishing prisoners for not following the new rules he had just made up. He would fly into a rage beating prisoners, then later apologize and ask them to forgive him.