Renaissance Technologies founder Jim Simons played a role in Robert Mercer giving up his leadership roles at the hedge fund, Bloomberg News reported.
Bloomberg said Simons urged Mercer to step down as co-chief executive because of concerns about backing Breitbart News. Citing people familiar with the matter, the report said Simons was concerned that Mercer's backing of the right-wing website was hurting morale at the world's most profitable hedge fund.
The report also said Simons was concerned that controversy surrounding Mercer's politics was hurting the hedge fund's recruiting efforts.
Mercer was a prominent backer of conservative causes and Donald Trump's presidential campaign. He also supported former White House adviser Steve Bannon's efforts at Breitbart.
Mercer sent a letter to investors on Thursday announcing plans to step down as co-chief executive and from the board of Renaissance Technologies. He said he will stay on as a researcher for the firm.
In a letter to his colleagues, Mercer also announced he is selling his stake in Breitbart News to his daughters.
Renaissance Technologies did not immediately respond to a request for comment.