Joseph Gruber was the older brother of Hans Gruber. They both had harsh natures, and when they relocated to Sisuphos for lack of a better place to make themselves known, took over Camp 3. However, Hans wished to make his own fortune, and eventually left to assume command of Camp 4.
Some time later a lode of ore was discovered between the two camps, and fighting broke out over the claims. When Joseph stole Camp 3's blue OCMT to claim the lode, Hans stole Camp 4's, and two vehicles engaged in an epic duel that resulted in both tractors' nuclear reactors exploding, killing both brothers and destroying the lode.