One of Citadel's top equity investors was let go from the firm, according to two people with knowledge of the matter.
Richard Schimel, who had headed the Aptigon Capital unit, left this week after a year and a half at the hedge fund, said the people, who asked not to be named discussing personnel moves. The reason was due to performance, one of the people said. There was also a difference of opinion on the future of the unit, another person said.
Citadel confirmed that Schimel had departed the firm as did the chief operating officer of the group, David Bonfili, and a "number of investment professionals."
"We are committed to the success of Aptigon Capital, and we will continue to recruit leading talent to the team," a spokesman at Citadel said.
Eric Felder has been named the head of Aptigon Capital and Reza Shahi will become the COO. Felder joined the firm last May to launch Fundamental Strategies and later assumed responsibility for Citadel's Global Credit business, Citadel said. He will continue to lead those businesses in conjunction with Aptigon.
Schimel had joined with much fanfare in July 2016 to start Citadel's fourth equity trading unit, based in Greenwich, Conn. Prior to Citadel, Schimel had co-founded Diamondback Capital in 2005 and grew it to a $6 billion firm at its peak. The firm shut down in 2012 after an insider-trading raid that caused investors to be nervous.
Schimel and Bonfili did not immediately respond to CNBC's request for comments. Business Insider first reported that Schimel and Bonfili had left.
Aptigon feeds into Citadel's main multi-strategy hedge funds, which returned 3 percent in January and 13 percent in 2017, a person with knowledge of the matter said. The firm does not break out Aptigon's performance, specifically.
Citadel, founded and run by Ken Griffin, manages $27 billion.