A person who backs, supports or champions a cause, activity or institution.
A benefactor; someone who donates to charity or some cause.
A person who produces articles published in a newspaper, magazine, online publication, etc.
A person (or thing) instrumental in the creation or growth of something.
A person who zealously promotes causes he or she believes to be matters of social justice, often for personal validation.
Used other than figuratively or idiomatically: see social justice, warrior; a social justice activist.