Original: Hummer was a brand of trucks marketed since 1992 by AM General when it began selling the civilian version of the M998 High Mobility Multipurpose Wheeled Vehicle (HMMWV or Hum-Vee).
Simplified: The design of the Hummer H1 is based on the military High Mobility Multipurpose Wheeled Vehicle (HMMWV - Humvee).