Which king of Lydia was proverbially rich?

Croesus, and Lydia has a better claim to fame than his wealth: it is where coinage was invented, around 600 BC. Standardised metal pieces stamped by a state to guarantee their weight and purity are a Lydian idea, and they arrived from a river running with electrum, a natural gold-silver alloy.

The story Herodotus tells is a set piece about hubris. Croesus asks the Athenian Solon who is the happiest man he has ever seen, expecting the obvious answer, and is given two obscure names instead - because, Solon says, no life can be called happy until it has ended well. Croesus then consults the oracle at Delphi about attacking Persia, is told that if he does he will destroy a great empire, attacks, and destroys his own.

That oracle is the definitive example of prophecy that cannot be wrong. Delphi's answers were routinely ambiguous enough to be correct either way, which is either fraud or an unusually sophisticated understanding of what people want from advice. Croesus, according to Herodotus, ended on a pyre calling out Solon's name, and was spared by Cyrus - though the archaeological and Babylonian evidence for what actually happened to him is thin and does not obviously match.