The Superiors were one title by which the powerful masters of Chris Cwej were known, alongside other names such as the Shadow People, the House-Dwellers, the Lords of Jewel, (PROSE: A Bright White Crack) Race of Temporal Supremacy, (PROSE: Ring Theory) and, more informally, Those Lot Up There. Influencing from the Base of Operations, they held domain over the Linear Universe. (PROSE: A Bright White Crack)
The term "mysterious superiors" was sometimes used to refer to the people of Iris Wildthyme (PROSE: From Wildthyme with Love, The Wildthyme Effect, AUDIO: Iris Wildthyme and the Land of Wonder) and the Doctor. (PROSE: Verdigris) Dionus once stated that members of the Great Houses that a "need to be Superior" seeded into "every morsel" of the breeding engines that "churned out" new members of their kind, making them "corrupt from birth", (AUDIO: Eternal Escape) with Rassilon also deeming the Time Lords a quintessential "superior species". (AUDIO: Homecoming)
On Earth, the term of "superior" could also generically be used to refer to individuals higher up in one's hierarchy than oneself, but not necessarily of a different species than oneself. The Brigadier had to deal with the whims of his own "superiors", (PROSE: Who Killed Kennedy) as did a guard who once captured Panda. (PROSE: Future Legend)
Having been responsible for the creation of the Linear Universe, they were notoriously unwilling to let any other species of cultures within their dominion recreate the scientific principles that gave them their power, as it would allow those lesser beings to challenge their rule. (PROSE: A Bright White Crack)
Using Chris Cwej as their agent
Iris Wildthyme had "mysterious superiors" who once tried to make Panda their Supreme Being. (PROSE: From Wildthyme with Love) Iris once lied to Alice Liddell that they had to stop travelling together because Iris' mysterious superiors would disapprove of the changes to history. (PROSE: The Wildthyme Effect)
Behind the scenes
Most everything about the treatment of the Superiors (as a distinct temporal faction rather than a generic term for high-ranking officials) in Cwej: The Series suggests they are intended to be the higher-ups of the Time Lord hierarchy, or simply the Time Lords themselves — mirroring the use of the phrase "mysterious superiors" to refer to Iris Wildthyme's kind in some of Paul Magrs's works.
However, the stories which feature the Superiors typically do not have the license to feature Gallifrey and its denizens directly, and especially in light of the Magrsian usage, they could just as easily be interpreted as the Clockworks, or indeed as the High Evolutionaries in general rather than specifically the Great Houses.