A very rich person.
H. Ross Perot's many successful business ventures have made him an American Croesus.
Croesus most often appears in the phrase "rich as Croesus," which means "extremely rich." Bill Gates, founder of Microsoft, could fairly be called "rich as Croesus." Croesus himself was a sixth-century B.C. king of Lydia, an ancient kingdom in what is now Turkey. He conquered many surrounding regions, grew wealthy, and became the subject of many legends.