The comic turns down dozens of TV and advertising requests, but agreed to appear in the new Greater Building Society Ltd commercial, after bank bigwigs approached him directly.
CEO Don Magin says, "Seinfeld topped our wish list of big stars we knew we'd never get.
He was stunned when Seinfeld, who earned $2 billion (£1.2 billion) from writing and starring in his own longrunning sitcom, said yes.
Magin adds, "He was wonderful. He gave us enough material for two dozen ads, along with his OK to use it all. Jerry doesn't need the money. He did it because he thought it was fun.
"We couldn't afford what he'd charge if he did it for money.".