When Donald Trump is in real trouble, he turns to Marc Kasowitz.

When a journalist dared to allege Trump was worth less than the billions he claimed; when women came out of the woodwork to accuse the future president of sexual assault; and when reporters sued for the unsealing of candidate Trump’s divorce records, Kasowitz—the prominent New York attorney with a shock of perfectly-coiffed white hair, a flair for the dramatic, and most important, a 15-year record of aggressive service—answers the call.

And so Kasowitz has answered it again, according to reports that the president hired the millionaire litigator to serve as his personal attorney in a Justice Department investigation into whether Trump’s campaign colluded with Russia to influence last year’s presidential election.

Several news outlets have pointed out that Trump’s retainer could pose a conflict of interest. Kasowitz employs Joe Lieberman, the former senator floated to be in the running for the FBI director job, a position that no one seems to want. Kasowitz’s firm also represents Russia’s largest bank, OJSC Sberbank, in a federal case unrelated to Trump. And until Tuesday, Kasowitz was representing Russian oligarch Oleg Deripaska’s company in an appeals argument, according to Neal Katyal, the attorney representing defendant Morgan Stanley in the case. “Bummer. I was looking fwd to it. I've not met him but by all accounts he is an excellent lawyer,” Katyal tweeted. Earlier this year, the Associated Press reported that Deripaska paid Trump’s former campaign manager Paul Manafort $10 million a year to lobby for Putin-friendly oligarchs and pro-Russian governments from 2006 until 2009.

Kasowitz—a Yale and Cornell University law school graduate, known as a trial lawyer who is willing to represent Davids and Goliaths alike—has little experience in criminal matters, but should former FBI Director Robert Mueller’s investigation uncover criminal activity, the 62-year-old litigator would likely bring on a team of attorneys better versed in criminal law. For now, loyalty seems to be Kasowitz’s best asset.

Kasowitz did not return requests for comment, but in January, told the Wall Street Journal, “Trump is a great client.”

He’s certainly dependable.

Trump first hired Kasowitz’s firm, Kasowitz, Benson, Torres & Friedman, in 2001, to restructure $1.3 million in bondholder debt held by his Atlantic City casinos.

In 2005, Kasowitz represented Trump in a failed suit against his Hong Kong partners, The Cheng Group, over accusations that they tried to sell a West Side property for less than it was worth, stiffing Trump in the process.

Later that year, Kasowitz demanded a retraction and apology from journalist Tim O'Brien who wrote in "TrumpNation" that Trump was worth as little as $150 million—a far cry from the net worth of $5 billion he liked to claim.

In a letter to O'Brien’s publisher Warner Books, Kasowitz wrote the book “contains out-and-out defamatory falsehoods concerning Mr. Trump, his business and his family," and demanded that Warner “immediately cease and desist further publishing and disseminating this book."

When Warner did not comply, Trump sued O’Brien for defamation to the tune of $5 billion. When the case was dismissed in 2009, Trump complained, “the libel laws in this country have never been fair.”

Kasowitz found greater success on Trump’s behalf in 2006, with a suit against condo board members at one of his properties, Trump World Tower. The bizarre lawsuit alleged the condo members had breached their contract and fiduciary duties in an attempt to take over the management of the property, and accused several members of threatening to murder other members, abusing condo employees, and walking around naked in front of staff.

Longtime attorney Alan Garten told the Wall Street Journal that Kasowitz has worked for Trump “countless times” behind the scenes, but with the 2016 announcement of his presidential candidacy, Kasowitz was set back to attack mode.

Last year, Kasowitz, threatened The New York Times with "prompt initiation of appropriate legal action" for the publication of 1995 tax records which revealed a $916 million loss that could have allowed Trump to avoid paying federal taxes for nearly two decades. And he successfully represented Trump against the paper of record and Gannett in their efforts to unseal Trump and ex-wife Ivana’s 1990 divorce records. In his motion against the unsealing, Kasowitz wrote, “There is simply no importance, overriding or otherwise, to unsealing the matrimonial records of a political candidate." Meanwhile, Ivana’s lawyer offered a different, but compelling argument: “Does anybody doubt that Donald isn't that nice to women?" her attorney asked the presiding judge.

And Kasowitz, who also counts disgraced former Fox News host Bill O’Reilly as a client, has defended Trump against claims of sexual harassment both in court and in the media.

In a letter to The New York Times following the paper’s publishing of claims from women who said Trump inappropriately touched them, Kasowitz threatened to sue, saying the article was “reckless, defamatory and constitutes libel per se.”

In a reply that quickly went viral, a lawyer for the Times wrote, “Mr. Trump has bragged about his non-consensual sexual touching of women. He has bragged about intruding on beauty pageant contestants in their dressing rooms. He acquiesced to a radio host’s request to discuss Mr. Trump’s own daughter as a ‘piece of ass.’ Multiple women not mentioned in our article have publicly come forward to report on Mr. Trump’s unwanted advances. 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.”

No lawsuit was ever filed.

Kasowitz does seems poised to appear on behalf on Trump against one accuser, however. Summer Zervos, a booted “Apprentice” contestant filed a lawsuit against Trump for defamation stemming from allegations that he made unwanted sexual advances. In March, Kasowitz filed a motion questioning the constitutionality of the lawsuit, “since it could “distract a President from his public duties to the detriment of not only the President and his office but also the Nation.” The case is still in its early stages.

Despite his imperfect track record on Trump’s behalf, Kasowitz has shown to be the kind of attack dog that Trump values most. It’s a tenacity that even former adversaries admire.

David Dean, the lead attorney for the plaintiffs in a case brought by victims of the 1993 Port Authority bombings against the New York City, in which Kasowitz represented the defense, recalled at the end of a nearly decade-long fight, holding Kasowitz “in high regard,” and described him in an interview with The Daily Beast as “smart, ethical, and hardworking.”

“I don’t respect his client,” Dean continued. “I’m appalled by what Trump is doing to this country, but Kasowitz I respect.”