Kronn

The Kronn are the villains in the Area 51 arcade game and it's sequel Site 4.

Area 51
0:500 A crashed alien probe is recovered and taken to a top secret military installation located in the remote Nevada desert: Area 51.

0:800 Shortly all contact is lost with the base and it is assumed an unknown alien force has taken control.

The Kronn infect the military compound along with the inhabitants. The only survivor sends an emergency distress signal to STAAR (Special Tactical Advanced Alien Response). Lieutenant Stephanie Grant, Sergeant Major Marcus Bradley, and a small group of other commandos are sent to Area 51. Upon arrival, they are greeted by an overwhelming force of Kronn life forms. They managed to destroy the aliens before seeking refuge in a nearby warehouse. Inside, there are more Kronn along with mutated humans who appear to be former employees. Every STAAR soldier annihilates a portion of the building until it is entirely vacant. Once outside, a truck drives away. One of the commandos, Peterson, is picked up by another member of the team. Together, they travel throughout the airfield section of Area 51. They encounter several zombies in moving vehicles. Peterson is retrieved by a chopper and taken directly to the administrative office. More powerful life forms are located there. Many of them are able to wield guns. Peterson, Grant, and Bradley are the only STAAR members present. The other commandos stayed behind to prevent an outbreak. The powerful Kronn life forms and STAAR members engage in hand-to-hand combat. STAAR is successful and enters a nearby elevator. Going down, they enter a computer room. Marcus activates the self destruct mechanism. Reduced to a lower status, the remaining Kronn and zombies retreat to an underground tunnel. STAAR follows them to a dead end. They encounter the original alien probe which is preparing to leave the planet. Together, the STAAR team shoot the probe until it explodes. Once the ship is destroyed, every member of STAAR evacuates the base before it explodes. The infestation of Area 51 ends.

Area 51: Site 4
The Kronn still exist. Its queen learns about the destruction of the alien probe that was sent to Earth. Furious, she and the remainder of her species travel to the planet. Upon arrival, they invade a scientific base and infect all of the inhabitants. Soon, STAAR detects the Kronn and dispatches several soldiers.