The Collaborative International Dictionary of English v.0.48:

Testator \Tes*ta"tor\, n. [L.: cf. F. testateur.] (Law)
   A man who makes and leaves a will, or testament, at death.
   [1913 Webster]

WordNet (r) 3.0 (2006):

testator
    n 1: a person who makes a will [syn: testator, testate]