William "Billy" Jensen Cottrell (born 1980) is a former Ph.D. candidate at the California Institute of Technology who was convicted in April 2005 of conspiracy and arson, associated with the destruction of eight sport utility vehicles and a Hummer dealership in the name of the Earth Liberation Front (ELF). He was sentenced to eight years in federal prison on arson charges and ordered to pay $3.5 million in restitution.