Republican vice presidential candidate Mike Pence spoke about his upbringing and family during a speech at the GOP convention July 20. (The Washington Post)

Donald Trump's running mate, Indiana Gov. Mike Pence (R), has been in public office since 2000, and yet a majority of voters don't know who he is.

Presumptive Republican presidential nominee Donald Trump picked Indiana Gov. Mike Pence (R) as his running mate. Here's what you need to know about Pence. (Peter Stevenson,Danielle Kunitz,Osman Malik/The Washington Post)

He'll make his second debut on the national political stage Tuesday night for the 2016 campaign's only vice-presidential debate. (His first was the Republican National Convention in July, where he joked about how few people know about him.) If you're like a majority of Americans, the top Mike Pence fact you know is that... he's one of the candidates in tonight's vice-presidential debate. So here's what you need to know about Donald Trump's running mate:

1. Yes, he's that guy from the last year's religious freedom debate.

Pence was already well known and respected in Republican circles when he was elected governor of Indiana in 2012. But he became a household name when he signed a religious freedom bill into law in 2015. Pence said it would extend legal protections to Indiana business owners who didn't want to participate in same-sex weddings, citing their religious beliefs; opponents argued that he was sanctioning discrimination.

The law got so much attention that at the 2015 White House correspondents' dinner, President Obama joked he and Vice President Biden were so close that "in some places in Indiana, they won't serve us pizza anymore."

After a week of taking heat from Democrats, LGBT activists, corporate America and the NBA, Pence signed an amendment, saying it's not okay to use it to discriminate against gay people. But that didn't quell activists' criticism of the law, nor did it boost Pence's tanking approval ratings.

2. He's a social conservative.

Pence is a devout evangelical Christian who regularly talks about his faith. (He likes to describe himself as "a Christian, a conservative and a Republican, in that order.") This spring, Pence signed into law one of the strictest abortion laws in the nation. Indiana is now the second state in the nation to ban abortions when the fetus has a disability, a law likely to be challenged in court.

But not all social conservatives are thrilled with Pence now: Some thought he backed off last year's religious freedom debate under pressure from liberal groups.

3. He's facing a competitive reelection.

At least, he was. Pence had to drop out of his reelection bid  — which may have been a good thing for him, given the religious freedom debate did Pence no favors in his reelection bid. Sensing an opportunity in a state that's been trending red lately, Democrats re-recruited businessman John Gregg, who has described himself as a "gun-totin,’ Bible-quotin,’ Southern Indiana Democrat." Pence and Gregg had matched up against each other before: Gregg lost to Pence in 2012 by 3.2 percentage points in an election in which Pence failed to get 50 percent of the vote. The race made our list of top 5 governor's mansions most likely to flip.

Instead, Indiana Republicans had to scramble to find a replacement four months before the election.

4. He was an early advocate for the tea party movement.

One of Pence's former advisers told NBC that even before the 2010 summer of discontent between conservatives and the establishment, Pence was tuned into the populist strain of the party. While in Congress, he voted against big spending bills that the tea party would come to loathe.

5. He endorsed Ted Cruz for president.

Cautioning that he wasn't "against anybody," Indiana Gov. Mike Pence revealed on The Garrison Radio Program April 29 that he plans to vote for Republican presidential candidate Ted Cruz in his state's May 3 primary. (WIBC/The Garrison Radio Program)

The political world's eyes were again on Pence this spring when his state had the potential to determine the winner of the Republican presidential primary. Pence came under scrutiny for being unusually quiet about who he'd support, a reflection of how the primary divided the populist strain of the GOP and its leaders. Four days before the primary, he finally, somewhat halfheartedly, said he'd be voting for Ted Cruz. But Pence tried to tack on a political insurance policy in case Trump won the state by adding, "I'm not against anybody," which may not have been the boldest pronouncement but certainly seems to have been the most politically savvy.

Trump did win Indiana by almost 20 percentage points. Cruz dropped out that night, and Pence said he'd support Trump as the nominee.

6. Paul Ryan likes him.

U.S. House Speaker Paul Ryan makes a statement to the media on Capitol Hill in Washington ruling himself out as a potential 2016 presidential candidate April 12, 2016. REUTERS/Yuri Gripas
Paul Ryan. (Yuri Gripas/Reuters)

Before becoming governor of Indiana in 2013, Pence spent six terms in Congress, where he served on committees that dealt with foreign affairs and technology and was generally well-liked and respected by his colleagues. Over time, he smoothed out his populist, tea party edges and rose to some of the highest ranks in the party. In 2008, his colleagues elected him to the House GOP's No. 3 spot, Republican Conference chairman, a job dedicated to shaping the party's messaging after it got slammed in the 2008 elections. (Republicans took back the House in 2010.)

Pence seems to have maintained his ties on Capitol Hill after leaving it. This week, House Speaker Paul D. Ryan (R-Wis.) said Pence is a "personal friend."

And before he came to Congress, Pence hosted a talk radio show, calling himself "Rush Limbaugh on decaf."

7. He once challenged John Boehner for his party's leadership spot in the House.

Pence may have harbored dreams of being House speaker himself. In 2006, while Republicans were still in the minority, Pence decided to run for the leader of the party against a veteran GOP congressman from Ohio, John Boehner. It didn't go so well. Pence, who positioned himself as the conservative in the race, lost in a vote among fellow House Republicans 168 to 27.

8. He's long been viewed as a potential presidential candidate.

In 2010, conservative activists at a Values Voter Summit voted Pence their top choice for a 2012 presidential candidate, a key test of grass-roots support (but not one that's necessarily indicative of success). Interestingly, Pence's 2016 veep competition, former House speaker Newt Gingrich, was also on that straw poll and came in fourth.

Pence's name was also floated in 2008 as a potential presidential contender. Pence decided to stay in Indiana and run for governor, where he eked out a win against Gregg.

9. He's got ties to the Koch brothers.

The billionaire brothers have so far stayed out of the presidential race, a sign they're no fans of Trump. But their 2016 involvement could change with Pence by Trump's side: The résumés of several of Pence's top aides also include stints with the Koch brothers' vast corporate and political networks.

And our crack money in politics reporter Matea Gold reported that the Koch brothers don't plan on getting involved in the presidential race even if their guy Pence is the GOP's No. 2.

10. He grew up as a Democrat.

And idolizing John F. Kennedy. Pence told CBN News in a 2010 interview: "It may be that I grew up in a big Irish Catholic family like he did. Maybe it was that my grandparents were so proud of the first Irish Catholic president." He even still has a box of Kennedy memorabilia.