This is part III of the Fallkniven knives
Rumour say that the S1 was initially developed as a knife for the Swedish Amphibious Corps, just like the F1 for the Airforce and the A1 for the Army. However the order never came and it was redesigned as a "Skogskniv", forest knife in Swedish.
There are some variations of this knife as well, but not that many.
S1 Early VG10
It was introduced early 1998 and came with either brown leather dangler sheath, kydex or cordura.
This sheath has a modified belt loop, normally it is leather as well.
S1 Late VG10
This might be a konvex all VG10 model like the F1 from 2002.
S1 Lam VG10
The current production model came in 2003. It initially came with the same sheath options as the older model, but nowadays it is either a black leather dangler or Zytel (like F1 and A1).
This version was also available as a bare blade, which can be found if you are lucky.