Gonarch

Gonarch, also known as the Titty Monster, is the mother of all headcrabs. She appeared in Reservoir G-Men.

Biography
Nathan Johnson travelled to Xen on a mission along with the Reservoir G-Men. They happened to stumble upon the Gonarch's lair, where his other two partners began shooting at her. Nathan took pity on the Gonarch so betrayed and killed his two teammates. He took Gonarch back to earth and had sex with her, and she gave birth to his headcrab baby, whom he called Laura.