Vortigaunt

Vortigaunts are a fictional extra-dimensional species in the Half-Life series by Valve Corporation. In Half-Life and its three expansions, Vortigaunts are frequently encountered by the player as hostile non-player characters. The Vortigaunts are depicted in Half-Life as being an enslaved race in an alternate dimension called Xen, subservient to a large Xen God called the Nihilanth, which itself is a slave to undisclosed masters. In Half-Life 2, the Vortigaunts have broken free of their slavery, and actively assist the player and other humans in resisting the Combine occupation of Earth.