The Collaborative International Dictionary of English v.0.48:

Benefactor \Ben`e*fac"tor\,n. [L.]
   One who confers a benefit or benefits. --Bacon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

benefactor
    n 1: a person who helps people or institutions (especially with
         financial help) [syn: benefactor, helper]

The Devil's Dictionary (1881-1906):

BENEFACTOR, n.  One who makes heavy purchases of ingratitude, without,
however, materially affecting the price, which is still within the
means of all.