social activist
activist focused on social issues
benefactor
person who gives some form of help to benefit a person, group or organization (the beneficiary)
syndicalist
person who promotes syndicalism, an economic system
moral entrepreneur
individual, group, or formal organization that seeks to influence a group to adopt or maintain a social norm
trade unionist
person involved in trade unions; member or supporter of a trade union
social reformer
person who works towards social reform
social justice warrior
pejorative term for a person expressing or promoting socially progressive views, including advocacy of feminism and civil rights