Gosh that’s hard. The easy answer is my father, since he shaped so much of who I am. But when you add the “changed your course” part, then it was the person who became my best friend when I was in college. She was a lesbian who I worked with, and she started me on a ten year career. She also caused me to change my attitude towards homosexuals, which began a complete change in the way I viewed the world in general and politics and religion in particular.
Another was a friend of mine who died of Leukemia at 16. We weren’t all that close, but his death made me question my religion, and was another key point in changing the way I viewed religion.
Next would be my son, whose birth completely changed my life in ways I had not foreseen and got me in touch with my emotions. He also teaches me patience every day.
And of course my wife, but her influence is more subtle, and she hasn’t precipitated any major changes in who I am in a person, just in my life’s trajectory.