Bermuda-based White Mountains Insurance Group Ltd. renamed Ray Barrette as chief executive officer, replacing Steve Fass, the man who succeeded him in 2005. Mr. Barrette will also assume the role of chairman from Jack Byrne, who is leaving that post for the second time in four years.

Eric Brielmann, a spokesman for the company, declined to comment on reasons for either departure.

Mr. Byrne, who first retired in 2003 because of illness, said in a statement yesterday it was “with great regret” that he must retire “completely”. Mr. Fass, who was asked to stay on, chose to retire from active management and will remain a director, the statement said.

Mr. Barrette, who joined White Mountains in 1973, retired in 2005. In August 2006, he returned as a director.

“The company has some terrific opportunities and I can’t wait to get started,” Mr. Barrette said in the statement. “Some tactics may change, but we remain focused on our mission of delivering superior returns to our owners.”