William McRaven, the retired U.S. Navy admiral who directed the raid that killed Osama bin Laden, told members of MIT’s graduating class Friday that they are the “real heroes” who will save the world from pandemics, war, climate change, poverty and racism.

McRaven, who delivered his address online to the Massachusetts Institute of Technology, said he grew up idolizing comic book heroes like Batman and Superman but came to see that “the heroes we need are not the heroes I had been searching for.”

“As I grew up and traveled the world, and as I saw more than my share of war and destruction, I came to the hard truth that Captain America isn’t coming to the rescue,” McRaven said. “You — the brilliant minds of MIT — you are going to have to save the world.”

McRaven, a native of San Antonio, graduated with a journalism degree from the University of Texas at Austin. After he retired from the Navy, he served as chancellor of the UT System.

In his advice on how to take up that mantle, McRaven told graduates that intellect and talent alone will not be enough. They need qualities he has observed in other heroes, he said, such as moral courage, perseverance and the willingness to sacrifice.

Real heroes are also humble, McRaven added, a lesson that coalesced during his years in the military.

“The crucible of war teaches you every day that you are not invincible,” he said, “that the enemy in bare feet and carrying only Kalashnikovs can sometimes defeat the best soldiers and the best technology in the world.”

McRaven was head of the U.S. Joint Special Operations Command in 2011 when a team of Navy SEALs killed bin Laden, the al-Qaida leader, in Pakistan. He also led the 2009 rescue of Richard Phillips, a ship captain who was captured by Somali pirates and later portrayed by Tom Hanks in a movie.

A former Navy SEAL himself, McRaven retired from the Navy in 2014 and led the University of Texas system until 2018.

His speech drew on “real heroes” McRaven said he has seen “on the battlefields in Iraq and Afghanistan, in the hospitals fighting COVID-19, on the streets keeping America safe and open.”

He said that, like SEALs, graduates will need to weather difficulty to reach triumph. And he said they should expect opposition.

“If you hope to save the world, you will have to stand by your convictions,” he said. “You will have to confront the ignorant with facts. You will have to challenge the zealots with reason. You will have to defy the naysayers and the weak kneed who have not the constitution to stand tall.”

McRaven, 64, had originally been scheduled to deliver his address during a ceremony at the school’s campus in Cambridge. But like dozens of other U.S. colleges, MIT canceled its campus graduation amid the coronavirus pandemic and moved it online.

This isn’t the first time McRaven has given a memorable speech. In 2014, his commencement address at the University of Texas at Austin went viral.