William "Bill" Sylvester Flanagan (April 9, 1901 – February 19, 1935) played for the Louisville Colonels of the National Football League during the 1926 NFL season. Flanagan was born on April 9, 1901 in Green County, Wisconsin, the son of William H.
Flanagan (1865–1939) and Marie Keegan Flanagan (1882–1972).
He attended Beloit Memorial High School in Beloit, Wisconsin.