Jimmy Grantz was a drug dealer who operated out of the Discount Inn and Ferdy's Bar. He was the boyfriend of Natalie, a barmaid at Ferdy's, and she took down his customer's orders on the bottom of beermats. He also dealt out of the Discount Inn, where Burt kept watch for anyone suspicious. When Burt saw Leonard Shelby taking a picture of the motel, he informed Jimmy, who came to know Leonard as "the memory guy" (on account of his amnesia). At some point, Leonard told Jimmy about Sammy Jankis.

Teddy, an undercover police officer, contacted Jimmy and set up a deal for $200,000 of amphetamines. Jimmy arrived at the meeting place but found Leonard there instead. He smacked Jimmy over the head with a tire iron, and made him strip off. Jimmy tried to bargain with Leonard, but he wouldn't listen, so Jimmy lunged out. After a struggle, in which Jimmy scratched Leonard's face, Leonard managed to strangle Jimmy to death. As he was dragged downstairs, in his final breath he whispered the words "Sammy", causing Leonard to realise he had killed the wrong man.

Later, an associate of Jimmy's, Dodd, attempted to retrieve the $200,000.

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