Mark Yates joined Cornerstone in July 2021 as a principal in the firm's Oklahoma City office. His experience in public policy includes working with various industries through statewide campaigns, legislative engagement, media relations, and public speaking. Mark has been successful navigating complex and challenging initiatives on behalf of the clean energy and agriculture industries.

Mark previously served as vice president at Advanced Power Alliance (APA) where he represented leading domestic and international companies in the renewable energy sector. While in this role, he managed the association's regional public policy strategy, communications strategy, and membership recruitment efforts. Mark served a major role in shaping legislative and regulatory policy within the most important energy region in the country.

Prior to APA, Mark worked at the Oklahoma Farm Bureau, where he led membership recruitment initiatives, mobilized a statewide grassroots campaign, and lobbied for rural issues on behalf of the nearly 90,000 farmers and ranchers.

Before his time with the Farm Bureau, Mark was a professional educator in the Oklahoma public school system for 11 years. Along with his teaching experience, Mark also had administrative experience serving as a federal programs director for Plainview Public Schools in Ardmore, OK.

Mark is a graduate of East Central University in Ada, OK and holds a bachelor's degree in History and master's in Secondary Administration. Mark and his wife Stacy reside in Edmond, OK where they are active in their community and have two children, Londyn and Steele.

Brian Hackler joined Cornerstone in November 2020 as lead of the firm's flagship office in Oklahoma City. He spent over a decade working for Sen. Jim Inhofe (R-OK). The last five years he served as his Deputy Chief of Staff and State Director. In this role, Brian managed and directed staff in Oklahoma City, Tulsa, Enid, and McAlester. Prior to this role, Brian served as a field representative for Sen. Inhofe covering Southwest Oklahoma. As a field representative, Brian gave legislative updates to local communities and helped constituents navigate federal issues.

Before joining Sen. Inhofe's office, Brian served in the United States Marine Corps from 2003 to 2007, where he played a key role in developing and carrying out daily strategic operations, including combat patrols, safeguarding government facilities and gathering intelligence. Brian was deployed to Iraq in 2004 and 2005, where he successfully contributed to the training and organization of Coalition Iraqi forces.

Brian also serves on the Board of Trustees for the Oklahoma City National Memorial & Museum. He currently resides in Edmond, Oklahoma with his wife and four children. He received a Juris Doctorate from the Oklahoma City University School of Law and a Bachelor of Arts degree in philosophy from the University of Central Oklahoma.