Senkaku was a very tall muscle bound brute who served ShiShio Makoto in his plans to overthrow the government of japan. To this end he captured a village for his master and turned the people there into slaves. He also exacted harsh punishment on those who resisted or tried to escape. In the process of terrorizing the village he killed Ei'ichirō parents. The boy would lead to his undoing as he escaped from the village and found help in the form of Kenshin Himura and Sanasuke Sagara.
With Shishio in the village he was ordered to fight Kenshin so ShiShio could obserev his techniques. The fool however was played by kenshin and after a heated chase his knee gave out from the stress and he was left helpless. Knowing that this meant his death he made a fianel attempt to kill Kenshin and kenshin revealed one of his techniques thus saving his life.
After this he is changed by Kenshin's act of kindness and becomes in ShiShio's eyes useless. Even though he is killed by Sojiro it is his change that causes doubt to creep into Sojiro's mind and leads to his defeat at Kenshin's hands.
Senkaku was a a super strong man who could charge like a bull for extended periods of time. He was also adept in the use of bladed weapons and torture.