William Sylvester Harley (December 29, 1880 – September 18, 1943) was a co-founder of the Harley-Davidson Motor Company. He was born in Milwaukee, Wisconsin in 1880, and received a degree in Mechanical Engineering from the University of Wisconsin–Madison in 1907.

Spouse: Anna Jachthuber, (2 sons, daughter)

He co-founded Harley-Davidson with Arthur Davidson in 1903 and served as chief engineer until his death in 1943.

Harley was the son of William Harley Sr. from Littleport, Cambridgeshire in England who emigrated to the United States in 1860.

In 1910 he married Anna Jachthuber, with whom he had two sons and a daughter.

He is buried at the Holy Cross Cemetery and Mausoleum in Milwaukee and was inducted into the Motorcycle Hall of Fame in 1998.

In 2003, a Harley-Davidson statue was unveiled in Littleport, Cambridgeshire, to commemorate the centenary of the famous motorcycle company. William Harley, the father of the company's co-founder William Sylvester Harley, had been born in Victoria Street, Littleport, in 1835, before emigrating to the USA in 1859.

Labor Hall of Fame

Because Harley, Arthur Davidson, William A. Davidson, and Walter Davidson "used and believed in its products and relied on the dedication of its employees to produce quality motorcycles," the four men were inducted into the Labor Hall of Fame.