"John Llewellyn Lewis (February 12, 1880 – June 11, 1969) was an American leader of organized labor who served as president of the United Mine Workers of America (UMW) from 1920 to 1960. A major player in the history of coal mining, he was the driving force behind the founding of the Congress of Industrial Organizations (CIO), which established the United Steel Workers of America and helped organize millions of other industrial workers in the 1930s. After resigning as head of the CIO in 1941, he took the Mine Workers out of the CIO in 1942 and in 1944 took the union into the American Federation of Labor (AFL)." From Wikipedia
John L. Lewis led several strikes during the Truman administration. Depsite this, Truman wrote in a note that he was "fond" of Lewis.
Read more about him at the American Federation of Labor and Congress of Industrial Organizations or in the Times' reporting on his from 1948 to 1952.
See the charismatic Lewis speaking to an audience.