Kid Parker was the leader of a band of mercenaries, which among others included Lonny and Wyatt. He was hired by Adam Hale, the leader of the Cultists, to sabotage the Robinson Crater Bridge and steal a shipment of Red Faction armaments being moved across it.
For whatever reason, Hale went back on this arrangement.
He was quickly tracked down to his hideout by a LAV belonging to the Red Faction. In the ensuing skirmish the rest of his gang were killed, though not without inflicting a heavy toll. He himself was killed shortly afterwards by Darius Mason.
Biography
Arrangement with Hale
Looking for the munitions required to wage a successful war against the colonists, Hale was eager for powerful weaponry at the disposal of the Colonist state in order to even the odds. He hired Kid Parker to waylay a train crossing the Robinson Crater Bridge and steal the weapons aboard.
Once the cargo had been acquired, however, the Cultist leader no longer needed it. It is possible that he had hacked into the Ultor database kept by the Archivists by this point and discovered what was hidden in it; reports relating to the MASTers Expedition of 2067, the Plague and the experiments of Axel Capek. He wouldn't need to win the war to achieve his aims, he just had to destroy the terraformer.
Stealing the Robinson Crater Weapons Shipment
Hale and his crew blew up the bridge, plunging the train crossing to the crater floor below. They killed any survivors they found, and then located the weapons, loading them onto the back of an eight-wheeler truck.
They fled the site of the Robinson Crater Disaster, but the incident had been picked up by a near by group of Red Faction.
Firefight with the Red Faction
Kid Parker killing Mariner.
Followed to the renedezous and stood up by the Cultists, Kid found himself arrayed against a small party of Red Faction soldiers lead by Darius Mason. Of his four assailants, two died in the course of the battle; one of which, Jim Mariner, he executed with his own pistol.
Nonetheless, his own men fell one by one until all that was left was himself. Darius killed him, crushing him between two magnetized floating rocks.