The Collaborative International Dictionary of English v.0.48:

Self-seeker \Self"-seek`er\, n.
   One who seeks only his own interest, advantage, or pleasure.
   [1913 Webster]

WordNet (r) 3.0 (2006):

self-seeker
    n 1: a person who places expediency above principle [syn:
         opportunist, self-seeker]