Rep. Paul RyanPaul Davis RyanRepublicans are avoiding gun talks as election looms The Hill's 12:30 Report Flake to try to force vote on DACA stopgap plan MORE (R-Wis.) will be facing off against conservative legal scholar Ted Olson as he prepares for his Oct. 11 debate with Vice President Joe BidenJoseph (Joe) Robinette BidenDems ponder gender politics of 2020 nominee Trump: Why didn't Obama 'do something about Russian meddling?' 2020 Dem contenders travel to key primary states MORE.

Mitt Romney's campaign confirmed Saturday that Olson has been serving as a stand-in for Biden as Ryan readies for the crucial debate. The two have held one prep session so far in the past week.

“Joe Biden has been in elected office for more than 40 years. There are few people in politics with more experience debating the issues than Joe Biden, so we are taking this process seriously," said Brendan Buck, a Ryan spokesman. "Mr. Olson is one of the most skilled, intelligent, and successful litigators in America — just the kind of opponent needed to prepare the Congressman for Mr. Biden.”

Olson served as Solicitor General under President George W. Bush, and was an assistant Attorney General in the Reagan Administration. A well-respected attorney, Olson has argued 58 cases in the U.S. Supreme Court, and has won over three-quarters of them. Currently in private practice at the firm Gibson, Dunn & Crutcher, he is also a recipient of the ABA Medal, the highest honor awarded by the American Bar Association.

Olson has also received attention for his work on same-sex marriage, breaking with many Republicans on the issue. In 2009, Olson helped file a federal challenge to Proposition 8, the California constitutional amendment that would ban same-sex marriage. Olson was joined in the effort by David Boies, the attorney who faced off against Olson as opposing counsel in the Bush v. Gore Supreme Court case that awarded George W. Bush the presidency. 

California courts ultimately declared the state's same-sex marriage ban to be unconstitutional, but have issued stays on same-sex marriages in the state until the appeals process is exhausted. The U.S. Supreme Court has yet to decide whether to hear the case.

Olson's work on the matter earned him, along with Boies, a spot on TIME Magazine's 2010 list of the world's 100 most influential people.

Paul Ryan's colleague on the House Budget Committee, Rep. Chris Van Hollen (D-Md.) is slated to play him in mock debates with Biden.