Uncovering a Letter From Ben Graham That’s Inspired Activists for Decades

In the pantheon of U.S. stockpickers, few are as closely studied as Benjamin Graham, professor to Warren Buffett and sage to value investors. But a letter he wrote in 1927, which some consider a seminal moment for activist investors, appeared lost when disciple Jeff Gramm starting asking for it.

Mr. Gramm, a hedge fund manager and now author, has long collected letters written by activist investors to companies. He even keeps a stack on his desk for reference. But he’d never seen a cop...