A singleton is an extraordinarily complex, advanced and expensive machine, built with a specific purpose. Singletons are similar to, but not the same as, combat drones. Singletons are far more complex and robust. Generally, singletons are not combat operatives, but they can be. Their chassis is designed to fulfill whatever their purpose is.
Each singleton is created with a single, unique Virtual Intelligence housed in it, tailored to the singleton's purpose.
In spite of their exceptionally advanced construction, hardy build and powerful VI, singletons are no more sapient than other VIs. But because of their chassis generally taking a bipedal, "people-like" construction, and their ability to perfectly mimic Kykr behaviour, anyone not familiar with singletons would never be able to tell that they're not sapient people, trapped in a mechanical body.
In spite of the name, "singletons" were originally meant to be mass-produced super-soldiers, capable of combining the best of both the digital and analogue worlds. They would be able of lightning-fast information processing, thanks to their combat computers, yet be able to recall, organize and consciously make decisions like a person, based on said information.
At the time of their invention, they were known as combat robots, not singletons. The term was later incorporated in more traditional security- and warfare drones, which can be equipped with a VI, but generally aren't.
It became rapidly apparent that the dream of fielding mass-produced super-robots for warfare was a pipe dream. The resources, cost and maintenance of such an army would be absolutely unfathomable. On top of that, there was extreme pushback from philosophers, AI-researchers and people alike, painting a doomsday scenario of hostile, sapient robots enslaving the Kykr, or downright wiping them out.
The idea was never scrapped and singletons gained their new name of being "one of a kind, unique". While singletons can be mass-produced, they are generally built one on one, for specific purposes. A variety of chassises exist that singletons can inhabit, and their neuromorphic computers are tailor made for the chassi and the singleton's purpose.
"Unique" is also a bit of a misnomer, as some singletons exist in pairs or even groups. In spite of this, each singleton has a unique number, or identifier, tied to them, often stamped somewhere visible on the chassis and as with all VIs, they tend to develop distinct personalities over time. This makes them, in effect, truly unique.
"Don't do this to me, Singleton."
"Your command is unclear, Derou. Don't do what?"
"This! This shit you're doing right now."
"And what would that 'shit' be, Derou?"
Derou let out a frustrated sigh and rubbed the back of his neck. "Don't get fucking uppity with me, Singleton, I swear..."
"I have a name. It would be appropriate for you to use it, Derou. Or would you like for me to refer to you as 'Dulzuun', so we are on a level playing field?"
A low rumble from Derou's throat gave the singleton just enough time to dodge the fist grabbing for its neck. It dodged with ease.
"Are you upsed, Derou?"
"I'm gonna fucking pick you apart and sell you for scraps, you piece of shit bucket of bolts!"
Derou jumped the singleton and started furiously punching it, dealing very little damage to its hardened chassis. The singleton, however, pretended to be damaged. Stumbling after each hit, intentionally whirring bearings and making grunting noises.
After a while, it fell to the ground and raised its hand toward Derou, as if to beg for mercy.
Derou stood above it, fists clenched, teeth gnashing and glared at it. After a few moments, he eased up and took the singleton's hand and pulled it back up.
"There. Don't you feel better?" The singleton placed a padded metal hand on Derou's shoulder.
"Yeah. I do. I'm sorry, mate. Didn't mean to lose my temper."
"You didn't. I intentionally triggered you. Your hormone levels were unstable. You needed the outlet. Let's get back to the job, shall we?"