Attitude is the most popular model in the Klein MTB line because it has been produced from 1990 to right Now (2004). The dimension of this bike has not changed as a hard tail MTB, but the details of the bike change dramatically. In my opinion, the time line of Attitude can be divided to three periods when I check the details of the bikes. So, I made a table as Attitude Chronology in order to explain the change of the details.
Attitude models could be separated to three generations.
The first period is 1990 to 1993. The first generation models had 6061 fat tubing, Klein precision BB, MC-1, ultra-oversized threaded headset, bulge-shaped internal cable in/outlet. This bike differs from other "normal" bikes apparently and all the features of the bike can fulfill the function in the mountain, so I think Klein could made the revolution in the MTB by producing Attitude despite the difficulties in maintaining by using specific tools.
The second period is 1994 to 1996. The second period models were developed from the first period in many details. MC-1 was changed to MC-2, Klein-sized threaded headset to AirHead system, bulge-shaped in/outlets to dimple-shaped ones, and Zip Grip seat post binder was introduced (*). This change could be an evolution of the first period models by accomplishing the lightweight. This is the peak point that Klein could climb up in the MTB world.
(*) Zip- Grip models were recalled because of the lack of binding force in 1994 season.
The third period is 1997 to Now (2004), after the merge by TREK. In this period Attitude has become the "normal" bike as the others gradually by cutting off the original parts. On the other hand, presumably, this change was made by TREK. "Normalized" Klein bikes can accept the standard parts such as Shimano BB, 1-1/8 Ahead set; therefore, the people have not to make the specific efforts to maintain post-TREK Klein. In the period, the Klein lost the differences from the other bikes, but got the popularity.
The first and second generation of Klein could make some kinds of influence to MTB, for instance, their seem to be over sized tubing, custom tubing, the sealed BB, the integral headset, the acceptance of 2.35 inch tires. Therefore, I'd like to insist that the MTB could change after the emerge of Klein Attitude.