Deputy Attorney General
Deputy Attorney General Klaassen was raised in Gillette and has lived in Cheyenne with his wife and three children since 2009. Before joining the Attorney General’s office, Klaassen served as United States Attorney for the District of Wyoming from 2017-2021.
Prior to his appointment as United States Attorney, Klaassen spent nine years as an Assistant United States Attorney, where he handled affirmative civil and financial litigation cases across the state. During that time, he was also elected to the Board of Trustees for Laramie County School District Number One, serving from 2014-2017.
Klaassen spent time early in his career in a variety of government positions in Washington, D.C. He was appointed by President George W. Bush to serve as Chief of Staff to the General Counsel for the Department of Homeland Security from 2007 to 2009. Prior to that appointment, he was General Counsel for the U.S. House Committee on Homeland Security from 2003 to 2007.
Klaassen has experience as an appellate law clerk for the Honorable Wade Brorby of the United States Court of Appeals for the Tenth Circuit, and worked in private practice as a litigation associate with the law firm of Latham & Watkins LLP. He received his B.S. in Finance, summa cum laude, from Oral Roberts University and his J.D., magna cum laude, from Notre Dame Law School.
Senior Assistant Attorney General
Sean is a native of northern Colorado, Sean earned a BA in History from Colorado State University in 2011 before earning a JD and Master’s in Public Administration from Indiana University in 2015. During law school, Sean earned a CALI Excellence for the Future Award for his performance in Water Law, and completed internships with the Law Reform Commission of Liberia, the City of Fort Collins, and the Indiana Attorney General’s Office. Sean began his career as an attorney for the Indiana Attorney General’s Office, advising numerous state agencies and boards on a wide variety of issues and litigating state collections cases. Sean is licensed to practice law in Indiana, Colorado, and Wyoming. In his spare time, Sean enjoys coaching wrestling and playing drums.