Lots of commencement speakers tell new graduates to use their gifts and make the world a better place.

Robert F. Smith, a multibillionaire who spoke to graduates at ​Morehouse College in Atlanta on Sunday, did a lot more than that. He pledged to pay off all 396 graduating seniors' student loan obligations, and urged the class of 2019 to "make sure [you] pay this forward."

His insanely generous gift was completely unexpected. Journalists were left scrambling to guess the total amount he was pledging, since it doesn't seem anyone had known or thought to calculate the how much the graduates actually owed ahead of time.

Estimates are running between $10 million and perhaps as much as $40 million. Here's how it unfolded:

On behalf of the eight generations of my family who have been in this country, we're going to put a little fuel in your bus. Now, I've got the alumni over there, and this is the challenge to you alumni.  

This is my class, 2019. And my family is making a grant to eliminate their student loans.

Those last 17 words left the audience stunned. In fact, it seemed to take at least a few seconds for people to comprehend that he'd truly said what he said. 

Morehouse College is an all-male college, and one of the 101 historically black colleges and universities in the United States. Smith, who had already pledged a $1.5 million gift to the college, is reportedly the wealthiest African America.

A graduate of Cornell University and Columbia Business School, he was a chemical engineer by training, working at companies like Goodyear Tire & Rubber and Kraft General Foods.

After earning his MBA, Smith worked at Goldman Sachs before launching Vista Equity Partners. He signed the giving pledge in 2015, promising to give half of his net worth to charity, focusing on things that support African Americans and the environment.

More than just his making a big donation, however, I think his speech will go down as one of the best commencement addresses in history -- and certainly the most memorable -- for at least three reasons:

  • The sheer generosity and focused wisdom of his gift. This kind of windfall could be life-changing for these students, perhaps just as much as getting their degrees. Not having to make student loan payments for the next decade or two frees people to make difference choices.
  • The magnitude of the larger problem. Student loan debt is a crushing burden in the United States for many people -- there's $1.5 trillion in unpaid debt, with the average 2019 graduate owing nearly $29,000 the day they get their degree. 
  • His immediate request that the class try to "pay this forward" in return. In fact, it wasn't even really a request -- Smith stated it as a truth that he assumed the class would live up to.

In a profile earlier this year, Forbes said it first "outed Smith as a billionaire in 2015," but he's apparently been a very private person who doesn't seek publicity. 

But after this gift -- and a related speech that will be remembered for generations -- he's about to become a lot more well-known.