participator, cohort, advocate, retainer, abetter _or_ abettor, sidekick, confederate, quisling, companion, colleague, precede, over, adherent, supporter, coadjutor, cooperator, collaborator, pardner, disciple, satellite, partisan, collaborationist, ally, partner in crime
assistant (part of speech: noun)
attorney, patsy, abettor, helpmate, hireling, aide-de-camp, proxy, junior, backer, associate, acolyte, underling, follower, extra, ancillary, accessory, benefactor, auxiliary, attendant, accomplice, helper, adjunct, agent, functionary, servant, deputy, aide, laborer, aider, stooge, minion, partner, subordinate, lieutenant, flunky, assistant, chaperone, menial, second, employee
servant (part of speech: noun)
- The messenger brought back word that the vicar would be delighted to come, and at the hour named the sound of wheels upon the gravel announced the arrival of Strawberry, the old mare, drawing behind her the vicar and his aged henchman, Reynolds, in the traditional vicarage dogcart. - "A Tale of a Lonely Parish", F. Marion Crawford.
- Is your amiable cousin's henchman a man to be scared off by our recent little encounter, do you think? - "The Stolen Singer", Martha Idell Fletcher Bellinger.
- It was strange familiarity for such an acrimonious old recluse, and even at the distance the attitude of Woodford's henchman seemed to indicate surprise. - "Dwellers in the Hills", Melville Davisson Post.