"Devils of Tau" but like, 40k, because I feel Warframe should share that name.
Named "Devils of Tau" by the Mechancium, are known as tempters of Machine Spirits, able to turn even the mightiest machines against the Machine God's wishes, but they are not born of the Warp.
Amalgam Intelligence* (known to the T'au as Mesme'vesa) are a rare machine intelligence, made of a "liquid metal" and an advance AI core, that have gained prominence among the Tau Empire seeking protection and employment, though some have also found employment with the Kyn, Eldar, and even Chaos.
The mystery of their own origin has been lost, but it is believed they are an AI Culture created by humanity during the technological height, an amalgam of Humanity's DAoT tech and Xenos tech.
Because of their DAoT origins, they have the ability to hack/override a lot of Imperial (and related) tech, particularly that which uses Servitor components, and their liquid metal bodies allow them to outright fuse/posses a wide array of technology into themselves.
Amalgams posses the innate knowledge on how to make more of their kind, however the components required are rare, in-demand, and/or expensive, so creating new ones is rare. Amalgams value the T'au and Kyn because of their more reliable production ability for this reason.
Mercury: an infiltrator agent working along side Water Caste, likes possessing "pleasure servitors" and servitors with advanced sensory to experience new things. Is offputting to many of their coworkers at first, but who's ultimate loyalty to the Greater Good is unquestionable.
Doug: A combat engineer working with a Sept Defence Fleet, Doug enjoys capturing trophies of Imperial Tech. The prize of his collection is the body he primarily uses for battle, that of a Techmarine. Enjoys the company of humans, especially children, running game nights for his local community.
*better/fancier name pending