The Ford Explorer is a series of SUVs introduced for the 1991 model year. The Explorer was Ford's four door SUV model, and was originally based on the Ford Ranger, but starting in 2011, the model used a proprietary unibody platform. Ford has produced the Explorer in a range of two or four wheel driver variants, as well as building the model in six generations. Rebadged versions of the Explorer have also been sold as the Mercury Mountaineer and Lincoln Aviator.