The Collaborative International Dictionary of English v.0.48:
Supplanter \Sup*plan"ter\ (s[u^]p*pl[a^]nt"[~e]r), n. One who supplants. [1913 Webster]WordNet (r) 3.0 (2006):
supplanter n 1: one who wrongfully or illegally seizes and holds the place of another [syn: usurper, supplanter]