In a major management change at Dimensional Fund Advisors, Gerard O'Reilly will become co-CEO of the money manager, replacing Eduardo Repetto, who will leave the position in late September, a spokesman confirmed in an email.
Mr. O'Reilly will also become chief investment officer of the firm, which reported $518 billion in worldwide assets under management as of June 30. He had been co-CIO, sharing the spot with Mr. Repetto, a 17-year veteran at Dimensional.
It is unclear why Mr. Repetto is departing. Efforts to reach him were unsuccessful.
The moves mark the second major management change at Dimensional in just seven months.
In February, Dimensional co-founder David Booth relinquished the co-CEO title that he shared with Mr. Repetto and became executive chairman. Dave Butler was named to replace Mr. Booth as co-CEO.
Mr. Repetto was seen as an heir apparent to Mr. Booth when he was promoted to the co-CEO position in 2010.
With the latest changes, Mr. O'Reilly will share the co-CEO spot with Mr. Butler.
In a news release, Mr. Booth said: "Eduardo has made tremendous contributions to Dimensional's success and our investment process."
Mr. Booth said of Mr. O'Reilly: "Gerard has been a vital member of both our investments and senior management teams over the past 13 years and I look forward to working with him in this new role."