William Thomas Piper Sr. (January 8, 1881, Knapps Creek, New York U.S. – January 15, 1970, Lock Haven, Pennsylvania) was an American airplane manufacturer, aviation businessman, oil industry businessman, and engineer. He was the founding president of the Piper Aircraft Corporation and led the company from 1929 until his death in 1970. He graduated from Harvard University in 1903 and later became known as "the Henry Ford of Aviation". The William T. Piper Memorial Airport in Lock Haven is named in his honor.
Piper served in the Spanish–American War and World War I, in the latter as a captain in the Corps of Engineers.
In 1980, he was posthumously inducted into the National Aviation Hall of Fame.