While this wasn’t my first mountain bike, it was the first one I put together myself, and the first that I paid for (insofar as you technically pay for anything when it’s through pocket money). The frame was aluminium, the hot new material at the time, purchased from one of those multi-page Merlin Cycles ads in MBUK. It was some kind of mass produced no brand affair, will no frills at all and probably on the heavy side, but at the time it felt pretty special.
As far as I remember I built the wheels too. Other features include solid cantilever brake fulcrums (which did basically sod all) and a rear derailleur tensioner to reduce chain slap. Suspension was provided by a knock-off Flexstem type thing which was comprehensively useless, later replaced by Rockshox Quadra 4s, which were marginally less useless, but still useless. The chainset was (I think) an old compact 2 ring road chainset that I got from somewhere, on which I screwed a 17 tooth cassette sprocket (via an adapter my Dad turned on his lathe), to give me a very spinny 2:1 lowest gear.
The frame actually lived a second life as part of a commuter bike up until relatively recently (2015 or so), but sadly a cracked chainstay finally killed it.