Final answer:
John L. Lewis was the most important labor leader of the 1930s and founder of the Congress of Industrial Organizations (CIO). He led the United Mine Workers and was effective at winning higher wages for miners.
Step-by-step explanation:
The most important labor leader of the 1930s and founder of the Congress of Industrial Organizations (CIO) was John L. Lewis. Lewis led the United Mine Workers and helped create the CIO, which was a federation of unions representing primarily unskilled and semiskilled laborers. He was known for his effectiveness at winning higher wages for miners but also drew criticism for his willingness to call labor strikes during World War II.