The Collaborative International Dictionary of English v.0.48:

Wrecker \Wreck"er\, n.
   1. One who causes a wreck, as by false lights, and the like.
      [1913 Webster]

   2. One who searches fro, or works upon, the wrecks of
      vessels, etc. Specifically:
      (a) One who visits a wreck for the purpose of plunder.
      (b) One who is employed in saving property or lives from a
          wrecked vessel, or in saving the vessel; as, the
          wreckers of Key West.
          [1913 Webster]

   3. A vessel employed by wreckers.
      [1913 Webster]

WordNet (r) 3.0 (2006):

wrecker
    n 1: someone who demolishes or dismantles buildings as a job
    2: someone who commits sabotage or deliberately causes wrecks
       [syn: saboteur, wrecker, diversionist]
    3: a truck equipped to hoist and pull wrecked cars (or to remove
       cars from no-parking zones) [syn: tow truck, tow car,
       wrecker]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "wrecker":
   animal, annihilator, anthropophagite, arsonist, barbarian, beast,
   biblioclast, bomber, brute, burner, cannibal, demolisher,
   depredator, despoiler, destroyer, dynamitard, dynamiter,
   exterminator, forager, forayer, freebooter, hun, hyena, iconoclast,
   idol breaker, idoloclast, looter, man-eater, marauder, nihilist,
   pillager, plunderer, raider, rapparee, ravager, ravisher, reiver,
   rifler, ruiner, sacker, savage, shark, spoiler, spoliator,
   syndicalist, terrorist, tiger, vandal, wild man