Congressman Cecil B. King (D-CA), left, and Senator Clinton P. Anderson (D-NM), right, along with SSA Commissioner Robert M. Ball, as Ball displays the new Medicare cards just issued to the two members of Congress. King and Anderson were the princpal sponsors of the Medicare legislation introduced in the Congress in January 1965. Their bill was the first enrolled in each chamber (H.R. 1 and S. 1) and was the basis for the start of the legislative process that eventually resulted in the Medicare program being passed that July. 1966 photo from SSA History Archives.
A detailed account of the development of the Medicare program can be found in Peter Corning's history "The Evolution of Medicare. . . From Idea to Law."