Mr. Walker has served as a Director since October 31, 2022. From 2011 to 2018, Mr. Walker was a member of the Board of Directors of Armstrong Energy, Inc., which operated mining, processing and loading facilities in the Illinois Basin, where he also served as the Chairman of the Conflicts Committee and a member of the Audit and Compensation Committees. From July 2009 through January 2011, Mr. Walker served as a Senior Vice President of Alpha Natural Resources, Inc., a publicly traded mining company, where he assisted with integration issues after the 2009 merger of Alpha Natural Resources, Inc. and Foundation Coal Holdings, Inc. (“Foundation Holdings”), which was a publicly traded mining company. From 2004 through July 2009, Mr. Walker served as the Senior Vice President, General Counsel and Secretary of Foundation Holdings, which was acquired in 2004 by a consortium of Blackstone Group, L.P., First Reserve Corporation and American Metals & Coal International, Inc. At Foundation Holdings, Mr. Walker oversaw all legal and regulatory matters related to the formation, financing, registration and initial public offering of the company on the NYSE. In his position as General Counsel of Foundation Holdings, he also had management oversight for the legal, environmental, land and government affairs functions at the company and had operational responsibility for the natural gas and coalbed methane business, which was developed into a successful operating asset under his leadership. From 1999 to 2004, Mr. Walker served as the Senior Vice President, General Counsel and Secretary of RAG American Coal Holdings, Inc., which was the predecessor entity to Foundation Holdings. From 1989 through 1999, Mr. Walker served in various capacities in the law department of Cyprus Amax Minerals Company, which was one of the largest integrated mining companies in the United States. From 1986 to 1989, Mr. Walker was a litigation and regulatory attorney for a private law firm. From 1981 through 1986, he held various positions within the law department of Mobil Oil Corporation in New York, New York and Denver, Colorado. Mr. Walker was also a member of the Board of Directors of FutureGen Industrial Alliance, Inc. (“FutureGen”) from 2005 through 2011, and in 2008, he served as the Chairman of the Board of Directors of FutureGen, which was a not-for-profit international alliance of major utilities and mining companies whose members worked with the United States Department of Energy to develop plans to design, build and operate a commercial scale power plant and associated carbon dioxide capture and sequestration project. Mr. Walker received a Bachelor of Arts degree from the University of Pennsylvania, where he graduated cum laude with distinction with a double major in Geology and Environmental Sciences, and a Juris Doctor degree from the University of Florida, College of Law, where he received various awards.