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.

Over about eighteen months, Heemeyer secretly armored a Komatsu D355A bulldozer with layers of steel and concrete. Granby town officials, neighbors of his muffler shop, the local press, and various other citizens of Granby had slighted Heemeyer in various ways, including zoning rules which impeded Heemeyer's ability to operate his muffler repair shop.

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.