Probably Team Fortress Classic. Hi to all nade and rocket jumping fans.

https://en.wikipedia.org/wiki/Team_Fortress_Classic

Never understood why it was "Classic"? Since it was the new version after the Quake mod.

Valve was working on TF2.. but it took years to be completed. It started as a more serious military shooter and became the lovely cartoon version later.

Classic is the version that was ported to the Goldsrc engine (which, itself, is a descendant of the Quake 1 engine) as a stand alone game.

TF2 is the same concept as TF/TFC, but turned into a full fledged game with its own soul.