Bill Ackman first heard about Warren Buffett when he was 20. Four years later, he read his first Berkshire Hathaway shareholder letter, and something clicked. “I was inspired to become an investor,” the hedge fund manager recalled.

Howard Hughes Holdings Inc.’s stock rose Monday as billionaire Bill Ackman reached a final agreement to acquire a controlling interest in the real-estate-development company that he plans to turn into a modern Berkshire Hathaway.