Michael Milken, a symbol of 1980s greed who went to prison for securities fraud and conspiracy, was at home in Encino, Calif., on Feb. 18 when he got a phone call from the White House. President Trump was on the line with good news: Mr. Milken had been pardoned.

Mr. Milken hung up, got in his car and drove to the home of his 96-year-old mother, Ferne Milken, according to Geoffrey Moore, Mr. Milken’s spokesman. When he shared the news, his mother burst into tears.

The presidential pardon “was a complete surprise,” Mr. Moore said. During the phone call, Mr. Trump claimed that the pardon was his idea and was based entirely on Mr. Milken’s philanthropic work, Mr. Moore said.

In fact, the pardon was the climax of a decades-long campaign on Mr. Milken’s behalf. And it was hardly a spontaneous gesture by a president acting alone. In announcing the pardon, the White House took the unusual step of releasing the names of 33 people who it said had provided “widespread and longstanding support” for pardoning Mr. Milken.