The Collaborative International Dictionary of English v.0.48:

Bungler \Bun"gler\, n.
   A clumsy, awkward workman; one who bungles.
   [1913 Webster]

         If to be a dunce or a bungler in any profession be
         shameful, how much more ignominious and infamous to a
         scholar to be such!                      --Barrow.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bungler
    n 1: someone who makes mistakes because of incompetence [syn:
         bungler, blunderer, fumbler, bumbler, stumbler,
         sad sack, botcher, butcher, fuckup]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "bungler":
   blockhead, blunderbuss, blunderer, blunderhead, boor, botcher,
   bumbler, clod, clodhopper, clodknocker, clot, clown, disregarder,
   dodger, dolt, fumbler, gawk, goldbrick, goof-off, gowk, idler,
   ignorer, klutz, looby, lout, lubber, malingerer, neglecter,
   negligent, oaf, ox, procrastinator, shirker, slacker, slouch,
   sloven, slubberer, slut, trifler, waiter on Providence, yokel