1. 
[syn: actor, doer, worker]
The Collaborative International Dictionary of English v.0.48:
Doer \Do"er\, n. [From Do, v. t. & i.]
   1. One who does; one who performs or executes; one who is
      wont and ready to act; an actor; an agent.
      [1913 Webster]
            The doers of the law shall be justified. -- Rom. ii.
                                                  13.
      [1913 Webster]
   2. (Scots Law) An agent or attorney; a factor. --Burrill.
      [1913 Webster]
WordNet (r) 3.0 (2006):
doer
    n 1: a person who acts and gets things done; "he's a principal
         actor in this affair"; "when you want something done get a
         doer"; "he's a miracle worker" [syn: actor, doer,
         worker]
Moby Thesaurus II by Grady Ward, 1.0:
22 Moby Thesaurus words for "doer":
   activist, ball of fire, beaver, big-time operator, bustler,
   busy bee, eager beaver, enthusiast, go-getter, human dynamo,
   hustler, live wire, man of action, man of deeds, militant,
   new broom, operator, political activist, powerhouse,
   take-charge guy, wheeler-dealer, winner