Chris Cwej's Superiors

The mysterious Superiors of Iris Wildthyme (PROSE: From Wildthyme with Love) and Chris Cwej (PROSE: A Bright White Crack) were the race who had established the Linear Universe. (PROSE: From Wildthyme with Love, A Bright White Crack)

Notably, other accounts described the Great Houses of the Time Lords as having played the role of creators of rational history (PROSE: Christmas on a Rational Planet) through the Anchoring of the Thread. That species did use Chris Cwej as an agent during the War in Heaven, (PROSE: The Book of the War) and Iris was one of their number. (PROSE: The Scarlet Empress)

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)

Nature
Chris Cwej thought of his Superiors as "the most complex pan-dimensional beings the Totality had ever produced". (PROSE: A Bright White Crack)

Culture
At one point in their history, the Superiors of Iris Wildthyme were ruled by a Supreme Being. (PROSE: From Wildthyme with Love) 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) Panda described them as perpetually "mysterious", although in other respects his writing to Iris on the subject of the species indicated he was somewhat blasé about them and their airs of grandeur. (PROSE: From Wildthyme with Love)

Creating the Linear Universe
Chris Cwej knew his Superiors played an immense part in the universe: they created the Linear Universe,and "wove Their likenesses into the biology of every being". (PROSE: A Bright White Crack)

Using Chris Cwej as their agent
The Superiors used Chris Cwej as their agent, having "stripped his flesh away" and turned him into an electronic consciousness whom they could reincarnate on cue. (PROSE: A Bright White Crack) They once sent him to the Psychosphere. (PROSE: Collective Unconscious)

Political unrest
Iris Wildthyme's mysterious Superiors nabbed Panda "once more", intent on making him into their Supreme Being. However, the Jane Fonda incarnation of Iris Wildthyme was present on their homeworld, and this allowed Panda to escape this unwanted responsibility by "cadging a lift" her. In a breach of common time-travelling practice, Panda was, at that point, at a different point in his timeline than Iris was in hers; indeed, he maintained a correspondance with the "correct" Iris throughout his travels with the fugitive. (PROSE: From Wildthyme with Love)

Destruction
Panda later wrote to Iris that he had reason to suspect that Iris's future incarnation, whom he described as "rather brutal," had "blown up" her Superiors during "something not very pleasant" to do with the Tim War, a chaotic space-time-bending fiesta. (PROSE: From Wildthyme with Love)

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 Iris Wildthyme and Cwej: The Series short stories suggests they are intended to be the higher-ups of the Time Lord hierarchy, or simply the Time Lords themselves. However, the stories which feature the Superiors typically do not have the license to feature Gallifrey and its denizens directly. Additionally, their identity is somewhat thrown into question by the existence of the Clockworks as a distinct but similar possible faction who could be described as "Iris Wildthyme's superiors".