William Paul Thayer (November 23, 1919 – May 6, 2010) was an American test pilot, flying ace, aviation executive, and United States Deputy Secretary of Defense during the Reagan Administration.

W. Paul Thayer was born November 23, 1919, in Henryetta, Oklahoma and attended high school in Wichita, Kansas.

Thayer flew a F4F Wildcat and became a flying ace, with six confirmed and four probable aerial victories, and nine further Japanese Air Force aircraft destroyed on the ground.

Thayer was deeply involved in the business community in the 1970s, serving as president of the United States Chamber of Commerce and as a member of The Conference Board.

He served as Deputy Secretary of Defense until January 4, 1984, when he resigned amid inquiries into charges of furnishing confidential stock market information, and was replaced by William Howard Taft IV.