Marvin John Heemeyer (October 28, 1951 – June 4, 2004) was an American automobile muffler repair shop owner who demolished numerous buildings with a modified bulldozer in Granby, Colorado, in June 2004. Heemeyer's machine was posthumously nicknamed the Killdozer.

Heemeyer held various grudges against town officials, neighbors of his muffler shop, the local press, and other Granby residents. Over about eighteen months, Heemeyer secretly armored a Komatsu D355A bulldozer with layers of steel and concrete.

On Friday, June 4, 2004, Heemeyer used the bulldozer to demolish the Granby town hall, the house of a former mayor, and several other buildings. He killed himself after the bulldozer became stuck in a hardware store he was destroying. No one else was injured or killed.