Thomas Usher, chairman of the board of Marathon Petroleum Corp. (MPC), will retire following the company's shareholder's meeting April 27, the company said. The board of directors has elected Gary Heminger, MPC president and CEO, to succeed Usher as chairman in addition to his current duties. Usher joined United States Steel Corp. in 1965 and played a pivotal roles in both the separation of Marathon Oil and U.S. Steel in 2001 and the spinoff of MPC from Marathon Oil in 2011. Heminger joined Marathon in 1975 and has worked in a variety of groups and functions, including auditing, marketing and commercial roles, and in Marathon's pipeline subsidiary. He held several executive positions in Marathon's downstream business, and was appointed president of MPC, a wholly owned subsidiary of Marathon, in 2001. Heminger is also chairman of the board and chief executive officer of MPLX GP LLC.