Co-Chief Executive Officer and Co-Chief Investment Officer, Dimensional Fund Advisors
Gerard O'Reilly is co-chief executive and co-chief investment officer of Dimensional Fund Advisors. He has shared the CEO role with Dave Butler since 2017.
O'Reilly studied at Trinity College Dublin, where he earned a first-class honors degree in theoretical physics and a master's in high performance computing, and then completed a PhD in aeronautics at the California Institute of Technology.
He joined Dimensional in 2004 and was named co-chief investment officer in 2014. In August 2017 the firm announced he would become co-CEO alongside Butler while keeping his investment role; Dimensional's Form ADV dates his co-CEO title to September 2017. The firm's other co-chief investment officer, listed in the same filing since February 2024, is Savina Rizova.
Dimensional, co-founded by David Booth in 1981, applies academic research to portfolio construction rather than picking individual stocks, and reaches most clients through financial advisors.
Sources · written 23 October 2026