Who are the Xen Species Aliens? "A collective of various extraterrestrial species that come from a border world-dimension called Xen, controlled by a powerful creature named Nihilanth. Many of the creatures were either bio-engineered or forced to live on Xen by the Combine Empire, who used Nihilanth as a puppet leader and hivemind to control a slave army. Years following the attack on Black Mesa, many species were scattered across the world following the Combine's Occupation."
god I love that Alien Grunt render so much
Picture credit to Operation Black Mesa.