Liberty Mutual Group of Insurance Companies in Boston today announced a series of leadership changes for three of the company’s four business units after the retirement of a key executive.

Chairman and President Thomas C. Ramey of Liberty International, who has led that business since 1998, will retire in mid 2009.

He will remain chairman until that time.

David H. Long, will succeed Ramey as president. Long is currently president of the company’s commercial insurance business unit. Also, J. Paul Condrin, currently president for personal lines, will take over as president of commercial lines; and Executive Vice President of Distribution for Personal Lines Timothy M. Sweeney, will become that unit’s president.

The changes will become effective Jan. 1.