R. Charles Tschampion, managing director of defined contribution plans at General Motors Asset Management and one of the architects of its investment strategy, and Susan Ezrati, GMAM chief client officer, retired April 1, according to Allen Reed, president and CEO. Mr. Tschampion joined General Motors' treasury department in 1968, managing the company's pension fund. In 1982, he was promoted to director of investment management for the pension fund and GM's investment management business. Ms. Ezrati joined GM in 1982 and moved to GMAM in 1998. Neither Mr. Tschampion nor Ms. Ezrati could be reached for comment.