Vortigaunts, sometimes known as "alien slaves". Their native home is the Xen border world, from which they travelled to Earth during the portal storms. They serve as frequently encountered enemies in the original game, and rarely-appearing allies in its sequel. In appearance, a Vortigaunt is somewhat humanoid with two legs and two arms, but has an additional arm protruding from its chest. This extra limb is a feature also found in the other bipedal, sapient species from Xen, including the Alien Grunt and Nihilanth. read more...