Leon D. Black, whose Apollo Global Management is among the world’s largest private equity firms, has gone to great lengths to distance himself from Jeffrey Epstein, the wealthy financier accused of sex trafficking.

In an email to employees last week and a quarterly earnings conference call and a letter to investors in the firm’s funds on Wednesday, Mr. Black described his relationship with Mr. Epstein as one largely limited to tax strategy, estate planning and philanthropic advice.

“I want to emphasize that Apollo has never done any business with Mr. Epstein at any point in time,” Mr. Black said in his letter, a copy of which was reviewed by The New York Times.

Most important, he wrote, “I was completely unaware of, and am deeply troubled by, the conduct that is now the subject of the federal criminal charges brought against Mr. Epstein.”