Who is Julián Castro?

San Antonio Mayor Julian Castro will be the first Latino to deliver a keynote address in the history of the DNC Tuesday. (REUTERS/Mayor Julian Castro's office/Handout)

Unlike Republicans, who chose a very famous — some say too famous — keynote speaker, Democrats have opted for a relative unkonwn, Julián Castro, the mayor of San Antonio.

Castro, 37, will be the first Latino to deliver a keynote address in the convention's history. The Atlantic has a run-down on the mayor. And here is a recent video conversation with him.

He is often compared to Barack Obama. "He’s young, telegenic and comes from humble roots (he was raised by a single mother and, like Obama, went on to receive a degree from Harvard Law School)," reports the Washington Post.

In San Antonio, he has recently asked voters to approve a tax hike to support a full-day prekindergarten education.

"A lawyer and former city councilman, Mr. Castro represents a new generation of Hispanic-American leaders in Texas from both parties who perhaps identify more with the second half of that descriptor than with the first, and who have broad appeal among minority and white voters," said the New York Times, in a profile of Castro.

His relationship with the president is a close one, and has been for years:

"...Castro was one of only five mayors in attendance and, at 35, the youngest. When his turn came to speak — the subject was the creation of green jobs — the president looked at him, midway down the long conference table, and said: “I thought he was on our staff. I thought he was an intern. This guy’s a mayor?”

The other participants — world-famous economists, environmentalists and politicians — burst into laughter.

"..of San Antonio, Tex.,” Castro said evenly.

Obama grinned. “I’m messing with you,” he said. “I know who you are," reported in the New York Times in 2010.