Executive leaves hedge fund Citadel

BOSTON, Sept 5 (Reuters) - A Citadel Investment Group LLC executive who ran an unprofitable credit investment group for the large hedge fund company has resigned, a person familiar with the matter said on Friday.

Joe Russell, who had been instrumental in making Citadel's investments in E*Trade Financial (ETFC.O: Quote, Profile, Research) this year and in failed hedge fund Sowood Capital last year, left the Chicago-based firm this week, said the source, who requested anonymity in order to speak freely about the personnel matter.

Russell ran the smallest of Citadel's three credit groups, and it was the only one that was not profitable. He resigned amid disagreements over how to manage the group, the source said.

Citadel is one of the world's biggest hedge fund firms, investing roughly $20 billion. (Reporting by Svea Herbst-Bayliss; Editing by Lisa Von Ahn)