They keep to themselves, the Callistans, and not without reason. The kind of work they’re hired to do is rarely pleasant; at the very least, the person they imitate or the place of business they infiltrate is in for a cash loss, if not a rapidly spreading rusty stain on the carpet. No one’s ever come forward to claim responsibility for engineering them; the Callistans themselves hold that they’re self-created and bred into existence over generations, or so they say to the sociologists who have managed to interview them.

But it’s obvious to everybody else that they’re engineered. Back in the day, before the bleeding hearts got all righteous about it, a number of Callistans that were iced during jobs were analyzed. Over 10,000 genes from outside what you’d traditionally think of as the human genome were floating around in there, including two kinds of chromatophores for natural camouflage (from the mimic octopus and chameleon respectively), jellyfish (to combat aging and free radical accumulation), salamanders (regeneration of injured parts), and many others.

All that means they have exceptional resilience and longevity, of course, but also no natural skin tone. Those same sociologists say the Callistans assume unnatural (for humans) colors to identify themselves to one another, with each lineage having its own distinct “normal” color and pattern. No hair of any kind, either–the better to blend in using creative wigs, since hair color can’t be changed on the fly. All that’s well and good, but what people reportedly find really repulsive about them is their lack of external ears and a nose; just slits there like you’d see on a burn victim (along with a lack of fingerprints). They substitute a variety of prostheses instead, the most elaborate of which can supposedly mimic the flesh tone around them.

In other words, somebody put an awful lot of loving care into engineering the Callistans for disguise and infiltration. That they don’t take credit for their work is probably a testament to the fact that their creations have long since surpassed and destroyed them.