Merck and Co. announced the retirement of its Chairman Richard Clark, effective Dec. 1. Kenneth Frazier, president of chief executive officer will succeed as chairman.

Clark has been with the company since 1972 and served as chairman since 2007. He was president and chief executive officer from 2005 through 2010. From the role of quality control inspector, he progressed through increasingly responsible roles. He left the company to join Merck-Medco Managed Care subsidiary as executive vice president and chief operating officer. He later became the chairman, president and chief executive officer of Medco Health Solutions. In 2003 Clark rejoined Merck as president of manufacturing division.