Minor human race apparently heavily engineered by the Ancients, the are split into two distinct 'species' one brainy one brawny. They cannot interbreed but are socially symbiotic.
They come from the spinward portion of the Trojan Reach sector - they first appeared in the Canadian Third Imperium fanzine, then MT and TD20, then GURPS Humans.
Look at Daryen's site for more on this.