Until the final minutes of their commencement ceremony last Thursday, the 1,200 graduates of the University of Massachusetts Dartmouth thought they knew what they would remember most about it: the supremely bad weather during the outdoor ceremony, where they sat drenched and shivering in a torrential rainstorm.

Then, as they prepared to collect their diplomas, their commencement speaker, Rob Hale, a billionaire philanthropist from Boston, returned to the dripping podium. He brought along two cash-stuffed duffel bags, he announced, and would hand every graduate $1,000 as they crossed the stage — $500 to keep for themselves, and $500 to give to any good cause.

“My friends and I were looking at each other like, no way,” Ali McKelvey, one of the students, said. “We were like, this has to be a joke.”

It wasn’t. Mr. Hale, the co-founder and chief executive of Granite Telecommunications, ranks as one of the country’s wealthiest people and most generous benefactors. He and his wife, Karen, gave away $1 million every week in 2022, to both well-known and unheard-of causes.

Still, as he told the graduates at UMass Dartmouth, he has never forgotten the experience of losing everything, when the first company he built went bankrupt in the dot-com crash more than 20 years ago.

“Honestly, have you guys ever met someone who lost a billion dollars before?” Mr. Hale, a part owner of the Boston Celtics, asked in his speech, which he cut short because of the rain.