William Frederick Rieflin (September 29, 1960 – March 24, 2020) was an American musician. Rieflin came to prominence in the 1990s mainly for his work as a drummer with groups (particularly in the industrial rock and industrial metal scenes) such as Ministry, the Revolting Cocks, Lard, KMFDM, Pigface, Swans, Chris Connelly, and Nine Inch Nails. He worked regularly with R.E.M. following the retirement of Bill Berry in 1997. He was a member of King Crimson from 2013 until his death in 2020.