Over the years, Mnuchin has been a Hollywood producer and a Democratic donor. Mnuchin has faced some controversy: A lending company on whose board he sits, the CIT Group, faces a housing discrimination complaint. "CIT is committed to fair lending and works hard to meet the credit needs of all communities and neighborhoods we serve," the company said in an e-mail to ABC News.
In a statement, Democratic National Committee communications director Adam Hodge criticized the selection of Mnuchin as a "slap in the face to voters who hoped he would shake up Washington." Hodge continued, "So much for draining the swamp," and characterized Mnuchin as a "billionaire hedge fund manager and Goldman Sachs alumnus who preyed on homeowners during the recession."
Here's everything you need to know about Mnuchin:
Name: Steven Terner Mnuchin (pronounced Min-OOCH-in)
Age: 53 (born Dec. 21, 1962)
Birthplace: New York City. Mnuchin comes from an influential New York family; his father, Robert Mnuchin, was a partner at Goldman Sachs and opened the Mnuchin Gallery on the Upper East Side.
Education: Yale University
What he does now: Steve Mnuchin is a co-founder, a co-CEO and the chairman of Dune Capital Management. He is a member of Trump's transition team executive committee and has visited Trump Tower in New York City several times since Trump was elected.
What he used to do: Mnuchin was a partner at Goldman Sachs, where he worked for 17 years, and left the firm in 2002. He then founded RatPac Dune Entertainment, which produced "Avatar" and the X-Men movies, among others. In 2009 he organized investors (including top Hillary Clinton donor George Soros) to buy the failed housing lender IndyMac and renamed it OneWest. OneWest was sold to the CIT Group in 2015. He also worked for Soros Fund Management, a firm founded by Soros.
Something you may not know about him: Mnuchin was a member of the exclusive Skull and Bones secret society at Yale, as were George H.W. Bush, George W. Bush and John Kerry.
Relationship with Trump
Trump named Mnuchin as national campaign finance chairman in May 2016. In an interview with Bloomberg, Mnuchin said he was with Trump at Trump Tower the night he won the New York primary and Trump asked him to join his campaign. "He's bringing a lot of people into the party who have not been part of the party in the past," Mnuchin said, according to Bloomberg.
In 2009, Dune Capital was among those that bought interests in a Trump construction project in Chicago. Trump subsequently sued to extend the dates of the loans, which the defendants, including Dune Capital, did not accept.
ABC News reached out to Mnuchin via Dune Capital Management about this lawsuit and is awaiting a response.
Positions on financial regulation
As treasury secretary, Mnuchin could be influential in the push — promoted by the Trump team — to alter the Dodd-Frank Wall Street regulations.
In a July interview with CNBC, Mnuchin said Dodd-Frank, passed in 2010, needs to be re-examined. "We're not taking a position on whether we support that or don't support it. We're saying a lot of things need to be looked at. We think Dodd-Frank needs to be looked at. Obviously there is an important concern of protecting depositors."
Possible flags for confirmation
Two groups in California, the California Reinvestment Coalition and Fair Housing Advocates of Northern California, recently filed a complaint with the Department of Housing and Urban Development against the CIT Group, alleging that it, as the successor to OneWest, failed to open a significant number of branches in minority neighborhoods and provide adequate loans in Southern California, including Los Angeles.
Mnuchin's mother invested with Bernie Madoff. She died in 2005 and left her sons $5 million. Securities Investor Protection Act Administrator Irving Picard sued them, claiming that $3 million of the money was stolen profits. The lawsuit was ultimately dropped.
In an interview with Bloomberg Businessweek, Mnuchin said of the lawsuit, "This was one of hundreds of cases that there was a decision on. There is nothing special about this case."
ABC News reached out to Mnuchin via Dune Capital Management about this lawsuit as well and is awaiting a response.
History of Democratic donations:
Although Mnuchin donated to GOP presidential candidate Mitt Romney, he has a history of donating to Democratic candidates, which may raise red flags for conservatives.
He has donated to the following politicians, according to the Federal Election Commission: Bill Bradley in 2000, Hillary Clinton in 2000 and 2005, Al Gore in 2000, Kamala Harris in 2016, John Kerry in 2004, Barack Obama in 2004 and 2007 and Chuck Schumer in 1998.