The impeachment inquiry of President Donald Trump moved in front of TV cameras Wednesday morning. Among those thrust into the spotlight during the public hearings was Steve Castor, a relatively low-profile lawyer with strong ties to the Philadelphia area.

Devin Nunes, the top Republican on the House Intelligence Committee, yielded much of his questioning time to Castor, who spent years interrogating Democrats as the chief lawyer of the House Oversight Committee when it was under Republican control.

Castor, a Philadelphia-area native, earned his bachelor’s degree at Pennsylvania State University and his MBA at Lehigh University before switching to law, gaining his degree from George Washington University. Prior to joining the Oversight Committee staff in 2005, Castor spent four years practicing commercial litigation in Philadelphia and Washington, according to a biography provided by House GOP staff.

For the last month, Castor has grilled witnesses as part of the closed-door hearings Democrats have held and made news when he openly said the alleged name of a whistle-blower during his questioning of Lt. Col. Alexander Vindman, a top Trump national security adviser.

» READ MORE: Live updates — Trump impeachment hearing reveals new detail about president’s pressure on Ukraine

“He has the longest-running institutional knowledge of most anybody on our side of the aisle,” Jason Chaffetz, a former Republican congressman turned Fox News pundit, told the Daily Beast.

“He has the institutional knowledge, experience, and prowess to be the guy in the hot seat,” Chaffetz, who chaired the Oversight Committee and worked closely with Castor, told the Associated Press. “Most of the public hasn’t seen him but for a photo of him in the background whispering to the chairman or a ranking member. But behind the scenes, he’s been doing these types of inquiries for years.”

Ahead of the hearings, Castor was reportedly unfocused on the public attention the investigation has garnered.

“I did ask him — I guess last night — ‘How do you feel about 11 million people watching you on television?’ And he said, ‘I’m going to look at the witness,’” former Oversight chairman and GOP Rep. Darrell Issa told the Washington Post.

» READ MORE: Inside the first Trump impeachment hearing: A resonant voice and damaging new details

Castor has been a critical player in several high-profile investigations, including the Justice Department’s selling of illegal firearms to track gun traffickers, known as Operation Fast and Furious, and the IRS’s alleged targeting of conservative groups.

Questioning for the Democrats

Democratic Chairman Adam Schiff is expected to lean on Daniel Goldman, the committee’s director of investigations. Like Castor, Goldman has been involved in the impeachment inquiry’s private questioning of witnesses.

Goldman served as assistant U.S. attorney in the Southern District of New York from 2007 to 2017, where he oversaw the prosecution of Russian organized crime networks. But he’s probably most well known by those outside the Beltway as a legal analyst on MSNBC.

» READ MORE: George Conway moves from Twitter to MSNBC: I’m ‘horrified’ and ‘appalled’

Schiff could also yield time to Daniel Noble, who was brought onto the Intelligence Committee in March as a senior counsel. Noble also spent time at the Southern District of New York prior to joining Congress, working with Goldman to convict Mikhail Zemlyansky in 2015 of racketeering, insurance fraud, and securities fraud.

Staff writer Jonathan Tamari contributed to this article.