William G. "Slicky Bill" Greene Jr.[1]: 44  (1812–1894) was an American businessman who was a close friend of Abraham Lincoln.

[1]: 29 By September 1831, Greene's parents lived 2 miles (3 km) southwest of New Salem; Greene, then age 19, was hired by recent arrival Abraham Lincoln to assist at Lincoln's mill and store.

[1]: 44  In early January 1833, Greene bought the inventory of Reuben Radford's store in New Salem for $400; Lincoln drew up and witnessed the mortgage.

Sons Carlin, McNult, Byrd, and Vance, and daughter Julia Greene, died before Gaines;[5]: 139  sons Scott and Frank and daughter J. S. Noble outlived Gaines.

[8] Greene died on June 30, 1894, and is buried in Greenwood Cemetery (East) in Tallula.