WASHINGTON — “Please call Leon Black.”

That phrase appears more than 300 times in the Jeffrey Epstein investigative files released by the Justice Department, some sent in emails to Epstein by his personal assistant. Black, for years a powerful billionaire Wall Street player, and Epstein had a business relationship stretching back decades.

“Leon, as you are well aware, there is little I won’t do for you or at least try to do as a friend,” Epstein wrote in one email to Black in 2014. “And a great deal that I have already done (both known and some things that will need to remain unknown.)”

Lawmakers are expected to press Black on Friday when he testifies before the House Oversight Committee investigating the federal government’s handling of the Epstein case. They are hoping to uncover more about the financial web Epstein wove that funded his sex trafficking operations and have said they believe Black may have played a role.

The former CEO of Apollo Global Management is the latest in a line of America’s powerful ruling class, including Bill and Hillary Clinton and Bill Gates, who have gone before Congress to discuss their ties to the man who preyed on women for years.

Black’s attorney, Susan Estrich, said in a statement to NBC News that Black had called for an independent investigation of his relationship with Epstein.

Estrich said a former federal prosecutor reviewed more than 60,000 documents and interviewed more than 20 people, including Black, as part of that investigation at the behest of Apollo and found that Black had only paid Epstein for tax and real estate planning advice for his family office.

“The investigation further found that Epstein’s work had been vetted and approved by best-in-class law and accounting firms,” Estrich said in the statement. “It also found that he had no awareness of the criminal activities that led to Epstein’s arrest in 2019.”

Black has denied any wrongdoing or knowledge of Epstein’s criminal conduct. He has said he deeply regrets “having had any involvement with him.”

“With the benefit of hindsight, working with him was a horrible mistake on my part,” he said in a statement when he stepped down from Apollo.

Black’s reputation has already been tarnished by his longtime association with the wealthy sex offender. He was forced out of the company he co-founded in 2021, after Apollo revealed Black had paid Epstein hundreds of millions for financial advice from 2012 through 2017, arguing he did so despite knowing that Epstein had pleaded guilty to soliciting prostitution from an underage girl in Florida in 2008.

Yet since the document dump of millions of files, questions have only grown about Black’s financial dealings with Epstein, who died by suicide in his cell in 2019 as he awaited a criminal trial in New York. His accomplice Ghislaine Maxwell was convicted in 2021 of federal sex trafficking charges.

The release of the Epstein files has prompted multiple investigations overseas as famous people and well-connected leaders around the globe were found to have associated with him. In the U.S., only New Mexico has launched a probe into the dealings on his secluded Zorro Ranch.

The political ramifications have been more swift; Republicans who pushed for the release of the files have seen their careers upended by President Donald Trump, who opposed the decision to make the trove public. Congress passed a law to force the release of the files.

Black and Epstein were introduced by a mutual friend in the 1990s. Epstein served as a director of Leon Black’s family foundation and later served as his financial adviser, reaping millions over the years.

Black’s phone number appears more than 200 times in the 3.5 million public files, and there are more than 100 instances of the phrase “Leon Black returned your call.” Many were sent by Epstein’s former assistant Lesley Groff.

In questioning by lawmakers on June 9, Groff was asked about Black and Epstein’s relationship.

“I thought they had a business relationship. I thought he was one of Epstein’s clients,” she said, adding that Black was a frequent visitor of Epstein’s.

Black and Epstein’s financial dealings had an alleged dark side. Black agreed to pay $62.5 million to the U.S. Virgin Islands in 2023 in order to be released from any potential action arising from a three-year investigation into an Epstein sex trafficking operation, according to the settlement.

Black was to be deposed in a lawsuit brought against Bank of America by survivors of Epstein’s abuse who argued the financial institution turned a blind eye to suspicious transfers Black made to Epstein from his Bank of America account, including $170 million for “tax and estate planning advice.”

The money, the plaintiffs alleged, was used to fund Epstein’s sex trafficking enterprise. Black said that wasn’t true. Bank of America agreed to pay $72.5 million in March without admitting any wrongdoing, and Black never testified.

Sen. Ron Wyden, D-Ore., part of the Senate Finance Committee, investigated Black for years and alleged Black may have funneled hush money payments to women, using Epstein as a middleman. Wyden said that in one email contained in the DOJ files, Epstein gave the location of a woman on Black’s payroll to a Russian government operative, and asked for suggestions on how to deal with her because she was attempting to blackmail “a group of powerful biznessman in New York.”

“Your relationship and business dealings with Jeffrey Epstein should be properly investigated by the federal government,” Wyden wrote in a letter to Black earlier this year.

Black, too, has been accused of sexual assault, claims he denies. One woman said in a lawsuit that Black had raped her at Epstein’s Manhattan townhouse in 2002. She eventually dropped the lawsuit and Black said he never met her. Another woman, a former model, accused Black of harassing and abusing her and argued he introduced her to Epstein. He countersued, and her lawsuit was dismissed.

One case remains open. Black was sued in 2023 by a woman who accused him of sexually abusing her when she was a teenager. A federal judge in April sanctioned the accuser, known as “Jane Doe,” her former attorney and the prominent law firm that had represented her for falsifying and potentially destroying evidence in the case. But the judge said the case could proceed.

Black’s attorney said in a statement after the ruling that the case never should have been filed. Estrich also said the firm Wigdor LLP had been warned the claims were fraudulent, but “Wigdor nevertheless continued the lawsuit and launched a media campaign to try to destroy Mr. Black in an attempt to shake him down for a financial windfall. Mr. Black refused because he knew the claims were false.”

Firm founder Doug Wigdor said in a statement that the firm was upset about the sanctions but pleased that its former client would get her day in court. Wigdor’s firm filed a separate claim in March accusing Black of targeting it for representing accusers; Black denies it. That lawsuit is ongoing.