The Collaborative International Dictionary of English v.0.48:

Solver \Sol"ver\ (s[o^]lv"[~e]r), n.
   One who, or that which, solves.
   [1913 Webster]

WordNet (r) 3.0 (2006):

solver
    n 1: a thinker who focuses on the problem as stated and tries to
         synthesize information and knowledge to achieve a solution
         [syn: problem solver, solver, convergent thinker]