Exponent – A person who supports an idea, belief or technique, or who performs an activity
The expert sword fighter defeated her opponent (exponent) using the technique that she supports to perform the activity.
Examples of exponent in a sentence
She was an exponent for animal rights and was against any form of animal testing.
After leaving the military he became an exponent of multiple charities that support veterans.
She was one of the leading exponents of karate and had been practising since she was able to walk.