Henry Lyle Adams (May 16, 1943 – December 21, 2020, Assiniboine-Sioux) was an American Native rights activist known as a successful strategist, tactician, and negotiator. He was instrumental in resolving several key conflicts between Native Americans and state and federal government officials after 1960. Born on a reservation in Montana and based in Washington state for much of his life, he participated in protests and negotiations in Washington, DC and Wounded Knee, South Dakota.