John K. "Jack" Leary Jr.

Served: 1990-1997

Previous experience: Deputy general manager of the Massachusetts Bay Transportation Authority in Boston, where he spent 24 years after beginning as a subway-train operator.

Thomas J. Irwin

Served: 1997-2001

Previous experience: Director of the Missouri Gaming Commission; assistant to then-St. Louis Mayor Vincent C. Schoemehl Jr.; deputy director of the St. Louis Development Corp.; campaign manager and assistant for the late George R. "Buzz" Westfall, then St. Louis County executive.

Larry Salci

Served: 2002-2007

Previous experience: President, American Passenger Rail Car Co. LLC; president, MK Transit Group, Chicago; president, Bombardier Corp., Washington; president, Budd Transit Group/Transit America, Philadelphia; general manager, Southeastern Michigan Transportation Authority, Detroit.

Robert J. Baer

Served: December 2007-present

Previous experience: President and CEO of UniGroup Inc., parent company of United Van Lines and Mayflower Transit; executive director of the Bi-State Development Agency (now Metro), 1974-1977; chairman of the Metropolitan St. Louis Sewer District; president of the St. Louis Police Board; chairman of the St. Louis Regional Convention and Sports Authority; chief of staff for then-County Executive Lawrence Roos.

John Nations

Begins: October 2010

Previous experience: Third-term mayor of Chesterfield; partner at Armstrong Teasdale law firm; member of the East-West Gateway Council of Governments; member, St. Louis County Municipal League transportation committee and Chesterfield Valley transportation development district; brokered public-private partnership to preserve bus service to west St. Louis County, 2009; headed the successful campaign to pass Proposition A transit sales tax.