Founders of Gallifrey

The Founders of Gallifrey, (PROSE: The Infinity Doctors) also known as the planet's Founding Fathers, (TV: Spyfall) were a group of legendary figures who were responsible for the creation of Time Lord civilisation. (PROSE: The Infinity Doctors)

The six sides of the Panopticon represented the six Founders, with a large statue of each Founder standing in each corner, (PROSE: The Ancestor Cell, The Infinity Doctors, The Quantum Archangel) but there was some debate as to who the six founders represented were. (PROSE: A Brief History of Time Lords)

claimed to the Thirteenth Doctor that the Founding Fathers of Gallifrey were responsible for "the lie of the Timeless Child", (TV: Spyfall) having falsified Gallifrey's histories to give the Time Lords a more noble and inspiring creation myth than the theft of regeneration from a helpless child. (TV: The Timeless Children)

Identities of the Founders
The Fourth Doctor once cited Rassilon as the singular founder of the Time Lords' "modern civilisation". (TV: The Deadly Assassin) The Doctor, while sitting on the foot of Rassilon's Founder statue in the Panopticon, once recalled that Rassilon was considered the greatest of the Founders, and sometimes called the "Father of Gallifrey". (PROSE: The Infinity Doctors) Though Omega was also a founder of the Time Lords' society, Rassilon had a higher position that made him, as the Eleventh Doctor put it, "Omega's boss." (COMIC: The Lost Dimension)

Many sources cited Rassilon, Omega, and the Other as being three central Founders, forming the ruling Triumvirate of early Gallifreyan history. (PROSE: Remembrance of the Daleks, Cat's Cradle: Time's Crucible, Lungbarrow, The Scrolls of Rassilon) Other sources indicated that two other Founders were Apeiron (PROSE: The Ancestor Cell, The Infinity Doctors) and Pandak. (PROSE: The Ancestor Cell, AUDIO: Time in Office)

Eutenoyar was revered by Gallifreyan cults alongside other founders. (PROSE: The Ancestor Cell) The Black Scrolls of Rassilon indicated that the three major contemporaries of Rassilon, Omega, and the Other were Thremix, Jelen, and Gimel. (PROSE: The Scrolls of Rassilon) Artron also had a large statue in the Panopticon. (AUDIO: Day of the Master)

The countercultural Nechronomancers worshipped the incomprehensible seventh founder, who was nameless, genderless, and historyless. (PROSE: And To Dust We Shall Return)

The Eremites' rites mocked the Great Houses' foundational first President, Urizen the Architect, whom they held to be the principal "culprit" for the Anchoring of the Thread and subsequent sterilisation of Great House culture. (PROSE: The Book of the War)

The information discovered by deep within the Matrix uncovered the existence of Tecteun, the first of the Shobogan species to travel in outer space, who had returned with the Timeless Child and extracted from the Child the secret of regeneration, thus laying the basis for the "genetic heritage" of the newborn Time Lord species. Tecteun, in a male incarnation, had later commanded great authority and respect in the newly-constructed Capitol. (TV: The Timeless Children) This stood in contrast to accounts in which Rassilon himself had discovered the secret of regeneration. (PROSE: The Legacy of Gallifrey)

While relaying the story of the Timeless Child to the Thirteenth Doctor, the Master additionally suggested that the Timeless Child themselves, through passing on their genetic template to the Capitol-dwellers, had, from "the Foundling", become "the Founder". The Master also claimed that the Timeless Child had eventually been rejuvenated and made to forgot their former life, becoming the Doctor as the Master knew them. (TV: The Timeless Children)

Statues of the Founders
The Founders were remembered in Time Lord society by being depicted in large statues in each of the six corners of the Panopticon, (PROSE: The Ancestor Cell, The Infinity Doctors, The Quantum Archangel, A Brief History of Time Lords) including Artron. (AUDIO: Day of the Master)

This was also the case in a version of reality where the Doctor lived on Gallifrey as a diplomat. There, a popular six-line logic puzzle nursery rhyme helped Gallifreyans remember the names of the statues and their achievements; the aformenetioned incarnation of the Doctor remembered the first half to be:
 * 'Neath Panopticon Dome
 * Rassilon faces Omega
 * But who is the other? (PROSE: The Infinity Doctors)

In a parallel universe created by the Quantum Archangel wherein the Sixth Doctor led the Time Lords in the War in Heaven, scaled-down replicas of the six founder statues existed in the miniature Panopticon on the Righteous Fist of Rassilon. These statues were made from marble and aeternium. Due to his actions in War, the Doctor no longer felt worthy to be in the original Panopticon, in the "heavy gaze of the six stone founders". (PROSE: The Quantum Archangel)

When Rassilon conquered Gallifrey with the help of Cybermen, he remodeled the Panopticon so that the giant statues were all of his own past incarnations. (COMIC: Supremacy of the Cybermen) Comparable statues of Rassilon across several incarnations existed within the Cloister Room of the Doctor's TARDIS. (TV: Doctor Who)

Behind the scenes

 * In the scene corresponding to the point in The Timeless Children where Tecteun's male incarnation stands alongside two other Time Lords in full high-collared regalia, the Timeless Children script release mentions that "we can assume [the other two] are Rassilon and Omega", suggesting a revamped version of the Triumvirate with Tecteun replacing the Other.