Citadel’s Griffin Taps Longtime Partner James Yeh as Co-CIO (Bloomberg) Ken Griffin promoted James Yeh to president and co-chief investment officer at Citadel, tapping a longtime partner to help run the fast-growing hedge fund firm alongside him. Yeh, 53, has been a key player at Citadel since he joined the Chicago-based firm in 1993 as one of its first employees. In his new role, announced on Wednesday, he will oversee the Global Quantitative Strategies business as well as the global fixed income and macro unit.