This story was updated at 7:30 p.m. ET
Donald Trump is expected to choose Indiana Gov. Mike Pence as his running mate, a source confirmed to NPR.
Pence has been governor of Indiana since 2013. Before that, he served as the representative of Indiana's 6th Congressional District from 2000 to 2012.
House Speaker Paul Ryan praised Pence Thursday: "It's no secret I'm a big fan of Mike Pence's. We're very good friends. I've very high regard for him."
He called Pence a "good movement conservative." Pence would help reassure conservatives, who have had their doubts about Trump, about what kind of president he would be. That's critically important as the Republican National Convention is set to kick off Monday in Cleveland.
Here are five things to know about Pence:
1. "A Christian, a conservative and a Republican, in that order"
Pence is a born-again Christian — he became one in college — and has put his religion in the foreground of his political persona.
"For me it all begins with faith; it begins with what matters most, and I try and put what I believe to be moral truth first. My philosophy of government second. And my politics third," Pence said in a 2010 appearance on the Christian Broadcasting Network.
Pence's strong Christian identity could help shore up support among evangelicals for Trump. It's a group critical to any Republican nominee's chances.
2. "Rush Limbaugh on decaf"
In the 1990s, Pence had a radio talk show called The Mike Pence Show and also did a Sunday TV show in Indianapolis. He described himself as "Rush Limbaugh on decaf," meaning while a conservative, he was not as bombastic as the popular Limbaugh, who hosts his own talk show. That's something people see as a positive for Pence on a Trump ticket given Pence's reputation for a low-key, unflappable demeanor.
3. "Confessions of a negative campaigner"
After losing early campaigns for Congress, he wrote an essay apologizing for running negative ads against an opponent, Rep. Phillip Sharp. The Indianapolis Star has reported Pence "swore off harsh political tactics." In the essay, Pence called for "basic human decency."
4. He's up for re-election and is in a tight race
Pence is in a heated re-election bout to hold on to his Indiana governorship. The latest polls show him polling just a few points ahead of his Democratic opponent, John Gregg.
But Pence can't run for both vice president and governor at the same time.
5. He gained notoriety for his role in the Indiana Religious Freedom Restoration Act
In 2015, he signed into law a controversial "religious freedom" bill, which spurred wide backlash. Critics said the bill could allow business owners to ban LGBT customers based on a claim of religious freedom.
After "business, civic and sports leaders ... strongly called for a fix to the legislation," USA Today noted, Pence later signed a revised version of the law.
But Pence appeared to back the bill in an interview on Fox in March 2015.
"Well let me say first and foremost, I stand by this law," he said. "But I understand that the way that some on the left, and frankly some in the national media, have mischaracterized this law over the last week might make it necessary for us to clarify the law through legislation. And we were working through the day and into the night last night with legislative leaders to consider ways to do that."