It was not until the late 1970s and early 1980s that road bicycle companies started to manufacture mountain bicycles using high-tech lightweight materials. Joe Breeze is normally credited with introducing the first purpose-built mountain bike in 1978. Tom Ritchey then went on to make frames for a company called MountainBikes, a partnership between Gary Fisher, Charlie Kelley and Tom Ritchey. Tom Ritchey, a welder with skills in frame building, also built the original bikes. The company's three partners eventually dissolved their partnership, and the company became Fisher Mountain Bikes, while Tom Ritchey started his own frame shop. The first mountain bikes were basically road bicycle frames (with heavier tubing and different geometry) with a wider frame and fork to allow for a wider tire. The handlebars were also different in that they were a straight, transverse-mounted handlebar, rather than the dropped, curved handlebars that are typically installed on road racing bicycles. Also, some of the parts on early production mountain bicycles were taken from the BMX bicycle. Other contributors were Otis Guy and Keith Bontrager.
Tom Ritchey built the first regularly available mountain bike frame, which was accessorized by Gary Fisher and Charlie Kelly and sold by their company called MountainBikes (later changed to Fisher Mountain Bikes then bought by Trek, still under the name Gary Fisher). The first two mass produced mountain bikes were sold in 1982: the Specialized Stumpjumper and Univega Alpina Pro.
Joe Breeze? Not in the UK!
The first UK foerunner must have been the Raleigh Bomber.... especially the fancy blue one.