Ranger is a Strogg without implants.
And here is the evidence.
- In Quake 1, the emblem of Ranger's military organization is a skull with stylized wings. In Quake 2 and 4, the same emblem represents the Strogg.
- Ranger is counterattacking an invasion of Lovecraftian monsters who come from a military teleportation device called Slipgate. In Enemy Territory: Quake Wars, the Slipgate is Strogg technology.
- In Quake Wars, the Slipgates are shaped like a Quake 1 symbol.
This universe is the same one where the Strogg exist, but Quake IV's
re-imagining of the universe especially ties in to this game.
Notably, the Strogg were able to develop their own [Super]-Nailgun and variant of the Thunderbolt and as mentioned above, the Strogg even have possession of Slipgate technology. The lack of the Quad Damage
in the single-player campaign is a consequence of the Stroggs' lack of knowledge about recreating the magic in this artifacts; they're probably captured and hidden away where they are never seen because the Strogg are attempting to reverse engineer them. On the other hand, the Strogg research into Dark Matter lead to major developments and may even be related to the Slipgate technology.