Source : Webster's Revised Unabridged Dictionary (1913)

Croesus \Cr[oe]"sus\ (kr[=e]"s[u^]s), n. [L., fr. G. Kroi^sos.]
   A king of Lydia who flourished in the 6th century b. c., and
   was renowned for his vast wealth; hence, a common appellation
   for a very rich man; as, he is a veritable Cr[oe]sus.

Source : WordNet®

Croesus
     n 1: last king of Lydia (died in 546 BC)
     2: a very wealthy man