Rosen has been brought in by Trump's longtime personal attorney, Michael Cohen, to handle the legal issues surrounding the so-called "hush" agreement that Cohen negotiated with the adult film actress known as Stormy Daniels, according to three people familiar with the arrangement.
Rosen, a partner in the firm LaRocca, Hornick, Rosen, Greenberg & Blaha, is a "pit bull" who will "aggressively fight and use his rhetorical and writing skills to get you a win," according to the firm's website. The firm is based out of The Trump Building on Wall Street in Manhattan's financial district.
According to the law firm's website, Rosen represents companies and "high net worth individuals in a myriad of areas of business and commerce," and also serves as an economic development official for his New Jersey hometown.
The dispute over the agreement with Daniels heated up this week, after she filed suit in Los Angeles over the validity of the contract that paid her $130,000 in exchange for remaining silent about her relationship with Trump. Her lawyer, Michael Avenatti, told ABC News this week that because Trump never signed the contract, he does not believe his client needs to honor it.
The hush agreement refers to Daniels throughout as "Peggy Peterson" or "PP" and Trump as "David Dennison" or "DD" in the copy of the document provided to ABC News by Avenatti. The line where where "DD" was supposed to sign is blank.
The dispute went into arbitration late last month, leading to a restraining order against Daniels.
Rosen first surfaced in public Wednesday, when he released a statement identifying him as Cohen’s attorney. In it, he said the arbitration found that Daniels had violated the agreement and it barred her "from, among other things, filing this lawsuit."
"We intend to pursue our recourse in the context of the arbitration as agreed to by the parties and continue to categorically refute the claims alleged by” Daniels, Rosen said.
Rosen has not yet responded to ABC News' requests for comment.
In addition to Cohen and Rosen, Trump has a team of outside lawyers also grappling with the special counsel investigation into alleged Russian meddling in the 2016 campaign.