You never know what can be found in a famous person’s typewriter. Joe DiMaggio’s old machine contained the cut-up shards of his expired bank card. Steve Soboroff, who bought the Yankees Hall of Famer’s typewriter in 2011, found the little pieces underneath the keys while cleaning it.

Mr. Soboroff also unearthed childhood photos of Ernest Hemingway in the writer’s 1926 Underwood Standard Portable. But Mr. Soboroff’s greatest discovery with these machines — and others, including typewriters belonging to Maya Angelou, Tennessee Williams, John Lennon and Shirley Temple — was a historical connection to great people.

“These are really hard for me to give up,” Mr. Soboroff said on a video call last week.

After 20 years of assembling what may be the greatest typewriter collection in the world, Mr. Soboroff is putting all 33 of his beloved machines up for auction. Owning them has been a privilege, he says, and each comes with a unique back story that helped fuel Mr. Soboroff’s passion.

Like when Mr. Soboroff backed out of a deal with the actress Angelina Jolie, refusing to part with Hemingway’s typewriter after she agreed to pay $250,000 for it. While reports at the time indicated Ms. Jolie was the one to walk away, Mr. Soboroff said he canceled the transaction when he learned that she intended to give the machine to her husband, Brad Pitt, for him to use. Mr. Soboroff might have allowed Mr. Pitt to bang away on Harold Robbins’s or Mae West’s machines, he said, but Hemingway’s typewriter was sacred.

“At that time, I could have used the money,” Mr. Soboroff said. “But nobody’s touching that one. Ernest Hemingway’s typewriter? No chance.”