In his commencement speech, in interviews and in his February manifesto, Zuckerberg is decidedly optimistic about all that. He's been saying he wants to make the world more open and connected for more than a decade now, and he doesn't relent.

He told the graduates how, when Facebook's investors and executives wanted him to sell the company early on, he resisted. "You see, my hope was never to build a company, but to make an impact," he said. But as a young CEO, he never explained this to his co-workers, and the subsequent fight "tore our company apart."

"I wondered if I was just wrong, an impostor, a 22 year-old kid who had no idea how the world worked," Zuckerberg said. "Now, years later, I understand that is how things work with no sense of higher purpose. It's up to us to create it so we can all keep moving forward together."Later in the speech, Zuckerberg's voice cracked with emotion as he talked about a high school student he mentors who is living in the US illegally. When Zuckerberg asked him what he wants for his birthday, the student started talking about others he wanted to help, and asked for a book on social justice.

Zuckerberg follows another famous Harvard dropout, Bill Gates, who spoke before its graduates a decade ago. Apple co-founder Steve Jobs, who dropped out of Reed College in Oregon, gave Stanford's commencement speech in 2005, reminding students to "stay hungry, stay foolish."

In addition to delivering the speech, Zuckerberg received an honorary degree, 12 years after dropping out of Harvard, and was subsequently introduced to graduates as "Dr. Mark Zuckerberg."

"If I get through this speech today it'll be the first time I actually finish something here at Harvard," Zuckerberg said. He did.

AP