The Collaborative International Dictionary of English v.0.48:
Truster \Trust"er\, n. 1. One who trusts, or credits. [1913 Webster] 2. (Scots Law) One who makes a trust; -- the correlative of trustee. [1913 Webster]WordNet (r) 3.0 (2006):
truster n 1: a supporter who accepts something as true [syn: believer, truster]