The Blue Bomber himself, also known as Dr. Light's lab assistant Rock. He's a pacifistic but courageous & selfless helper robot that was modified into a super fighting robot to stop Dr. Wily's world domination schemes. With his dog Rush modified into the Rush Roadstar, he entered the Battle & Chase competition to help fund for Dr. Light's destroyed computer with the high zenny prize. 

You can choose to do whatever voice you have in mind for Mega Man as long as it gets the core of his dedicated and heroic personality. Though for me, something along the lines to his voice in Mega Man Powered Up would be most preferable.