contributor

A benefactor; someone who donates to charity or some cause.

“I am a longstanding financial contributor to Amnesty International.”

A person who backs, supports or champions a cause, activity or institution.

“He was a regular contributor to Greenpeace protests.”

A person (or thing) instrumental in the creation or growth of something.

“With her strength and intelligence, she was an important contributor to the victorious effort.”

A person who produces articles published in a newspaper, magazine, online publication, etc.

“William Safire has been a notable contributor to the op-ed pages of the New York Times for many years.”