One of the key men at the world's biggest hedge fund is stepping down.

Bridgewater Associates co-CEO Jon Rubinstein is stepping down and transitioning to an external advisory role in April after 10 months on the job, the firm told clients in a note Wednesday.

"While over the last ten months Jon has helped build a plan to re-design our core technology platform and has brought in a group of extremely talented executives to build out our technology leadership, we mutually agree that he is not a cultural fit for Bridgewater," Bridgewater founder, chairman, and co-CIO Ray Dalio wrote in the note.

This isn't the first time cultural problems have been cited for a senior staffer's departure. FBI director James Comey was previously the firm's general counsel, and he said he had difficulty conforming to Bridgewater's culture, according to a Wall Street Journal report last year.

The announcement was one of several Dalio made in the note, which also revealed that -- in keeping with the 10-year succession plan begun in 2011 -- he would be transitioning out of a co-CEO role, and passing it to president David McCormick, who will be sharing the role with longtime CEO Eileen Murray.

Last year Dalio told Business Insider why he hired Rubinstein, a former Apple executive who worked with the late Steve Jobs for 16 years.

"There are two things I look for when assessing people," he said then. "First, do we share similar values of producing greatness through thoughtful disagreement? Jon worked next to Steve Jobs for 16 years doing that, and he clearly wants to do that with us. Then I look at the skills we need. Jon has a world-class track record as both a leader of people and a shaper of technology, both of which we need."

Bridgewater's culture is famously unusual and difficult, and its leadership team has likened it to "an intellectual Navy SEALs." In its world of "radical transparency" and "radical truth," employees rate each other's performance in real-time on proprietary iPad apps, and nearly all meetings are recorded to be available for scrutiny. The company reports that 30% of employees leave the company within their first two years.

Bridgewater has now posted the full memo to clients on LinkedIn .

This post originally appeared on Business Insider.