What is another word for "cooperator"?

Roget's Thesaurus (1911) lists these synonyms for "cooperator": abettor, accessory, accomplice, adherent, adjunct, adjutant, adjuvant, advocate, after, ally, alter, angel, assistant, associate, auxiliary, backer, candle, champion, clerk, coadjutor, coadjutrix, collaborator, colleague, complice, confederate, confidant, confrere, court, criminal, dupe, ego, entertainment, fact, friend, genius, girl, gopher, guardian, hand, handmaid.