One of the key men behind Bill Ackman's bet on Valeant is leaving

One of Bill Ackman's key researchers on Valeant is leaving Pershing Square and plans to launch a startup focused on reducing healthcare costs.

Jordan Rubin, a member of Ackman's 10-person investment team, is leaving Pershing Square Capital Management in the coming weeks after seven years at the firm.

As an investment analyst, Rubin, 32, contributed to positions including Valeant Pharmaceuticals International, Zoetis, Allergan and Family Dollar.

"I think extremely highly of Jordan," Ackman told Business Insider. "He's a very talented, hard working, smart person, and I think he's going to be enormously successful with his new venture."

Rubin and Bill Doyle, who also recently left Pershing Square, led the research that resulted in Pershing Square's "partnership with Valeant in its efforts to merge with Allergan," according to a 2014 letter filed with the SEC.

Rubin also features heavily in 818 pages of Valeant-related information released by the US Senate in connection with its investigation into the pharmaceutical company's business practices.

Several emails from Rubin to former Valeant CEO Mike Pearson were published in the document dump, along with other emails from Ackman where Rubin was CC'd in.

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Rubin's departure comes as Pershing Square hits a rough patch in performance, largely from positions like Valeant, which has dropped in value this year, partly over concerns about the company's drug price hikes.

The Pershing Square L.P. fund fell -16.2% last year after posting 36.9% gains the year before, according to a Pershing Square document. Pershing Square Holdings, a publicly traded vehicle that is a proxy for Ackman's hedge fund, is down -17.8% through August 16.

Rubin joined Pershing Square in 2009 after a stint at Goldman Sachs, where he worked as an analyst in the special situations group.

In a statement to Business Insider, Rubin said he was "grateful for the opportunity to have contributed to many profitable and innovative investments at Pershing Square" and that he is "excited to begin the next stage" of his career.

"I hope to follow in the footsteps of other successful Pershing Square alumni who have chosen an entrepreneurial path," he said, adding that he plans to continue to invest in Pershing Square's fund.

Rubin is partnering with an unnamed healthcare entrepreneur for the startup, which will target reducing healthcare costs and is set to launch later this year.

Other prominent staffers have also departed the firm in recent months. In May, the firm announced that Bill Doyle, who was also behind the Valeant bet, was leaving.

Paul Hilal, Ackman's former second in command, left last year and is in the early stages of starting his own hedge fund.

Earlier this year, Pershing Square also cut more than 10% of staff, mostly in operations, due to technological changes.

But there have also been additions. Jenna Dabbs, a former federal prosecutor in New York who was hired last year as senior counsel, joined Ackman's investment staff earlier this summer, making her the first woman ever on the team.