The selection of Kasowitz comes amid growing legal trouble for Trump over the Russia investigation and his controversial ouster of Comey. After his removal, The New York Times reported Comey kept contemporaneous notes about conversations with Trump in which the president allegedly asked him to drop the investigation into his former national-security adviser, Michael Flynn. Those memos, as well as other public remarks by Trump about Comey, could potentially prompt a federal investigation into obstruction of justice on the president’s part.

Kasowitz is a founding partner of Kasowitz Benson Torres, a high-profile law firm with headquarters in New York City. His profile on its website describes him as an “uberlitigator” and “the toughest of the tough guys.” Established in 1993, Kasowitz Benson primarily handles litigation for large corporations and real-estate cases. It’s also drawn attention for its close ties to the president. The firm was previously known as Kasowitz, Benson, Torres & Friedman, for example, until David Friedman, who headed the firm’s bankruptcy division, resigned to join the Trump administration as the U.S. ambassador to Israel.

Kasowitz himself has a long history of working high-profile cases, ranging from tobacco company lawsuits in the 1990s to those of large banks and insurance companies in recent decades. In the mid-2000s, he represented the Port Authority of New York and New Jersey in a negligence lawsuit brought by victims and their families over the 1993 World Trade Center bombing. More recently, he signed on in March as lead attorney for OJSC Sberbank, one of Russia’s largest state-run banks, in a fraud lawsuit involving the institution’s takeover of a granite-mining company.

But he’s perhaps best known for his long history representing Trump in a multitude of legal matters. In that role, he’s been an aggressive defender of the real-estate businessman’s interests and reputation. At times he’s played a role in the Trump University fraud litigation saga, which ended in January with a $25 million settlement from Trump. In 2006, he sued Trump biographer Timothy O’Brien on his client’s behalf, claiming the author had inaccurately described Trump’s net worth as a paltry $1 billion. (A New Jersey court eventually tossed out the lawsuit.)

Another high-profile incident came during last year’s presidential campaign when the Times published interviews in October with two women who accused Trump of inappropriately groping them years earlier. Trump immediately threatened to sue the newspaper in retaliation. In a letter to the newspaper on Trump’s behalf, Kasowitz called the article “per se libel” and asked the newspaper for “a full and immediate retraction and apology.”

David McCraw, the Times’s legal counsel, responded by noting that American libel law exists to protect a person’s reputation from malicious attacks. “Nothing in our article has had the slightest effect on the reputation that Mr. Trump, through his own words and actions, has already created for himself,” McCraw wrote. If Trump believed the First Amendment would allow him to punish the Times for its reporting on a subject of national interest, he added, “we welcome the opportunity to have a court set him straight.” No lawsuit has been filed.