After Weyland-Yutani acquired several Xenomorph specimens, the head scientist of the project began genetically manipulating the creatures in order to create a suitable bio-weapon. This became known as the K-Series which were visibly different from the standard breed due to its yellow skin tone.
Initial tests of the newly developed K-Series forced the creatures to fight a small brood of standard Xenomorphs but the original strain proved superior in the battle. The K-Series would continue to survive but an attack on the research facility by the Predators caused a breach in containment resulting in the K-Series being freed. A Queen was created which continued laying more eggs for the species to develop.Colonial Marines, Predators and a Xenomorph Hive; the K-Series Aliens would be exterminated bringing a quick end to the race. (Aliens versus Predator: Extinction).
These "K-series" Aliens behaved like normal xenomorphs as they gathered hosts and had a queen that affected the hive. They also had all the same castes as the normal xenomorphs though with a different color.
- The K-Series likely stands for "Kadinsky Series"