The following individuals are considered by New Gallifrey to be the "official" founders of Gallifrey, although there may be some debate as to who founded what chapter and who counts as a founder at all within the fandom. Most notably, The Other is considered a founder of the Patrexean Chapter as opposed to the CIA, as recovered memory from members of New Gallifrey has indicated that they were in fact the same person as Eutenoyar, and "The Other" was simply their titled/renegade name. As many of the other founders' names are adjectives, the names officially listed for the founders may all be titled or renegade names in the original Gallifreyan language, either approximately translated or transliterated to English.
rassilon
The Seal of Rassilon in Prydonian colors.
Rassilon, otherwise known as the first Time Lord and the founder of Gallifrey, is a legendary figure in Gallifreyan history. Many important Gallifreyan artifacts are named after him, most notably the Presidential Regalia. He founded the Prydonian Chapter. Many versions of Gallifreyan history see Rassilon as unquestionably corrupt, but most members of New Gallifrey do not see him this way, either valuing his contributions or understanding why he took the actions he did in canon.
omega
The Seal of Omega in Arcalian colors.
Omega is largely considered the second-most significant founder of Gallifrey, and is also considered the first Time Lord by many. Founder of the Arcalian Chapter, before the Omega Crises he was very academic and focused on technology. In many timelines, Rassilon and Omega were either close friends or partners, and many members of New Gallifrey had made jokes about how "local king (Rassilon) can't stop promoting his boyfriend (Omega)" because of the political prowess of the Arcalian chapter, which would likely not have been as significant if Omega had not been made politically important. Omega is one of the letters in the Greek alphabet.
the other/eutenoyar
The Seal of The Other/Eutenoyar in Patrexean colors.
The Other, otherwise known as the founder of the Patrexean Chapter, is the final founder in the Upper Triad, which is the group of the "most important" founders of Gallifrey. Truly, all founders of Gallifrey were very important, as they all founded the chapters that New Gallifrey members are a part of today. The Other had a personality very quirky and similar to that of the Doctor, meaning that in many different canons, they were the same person as the Doctor. Regardless of which canon or fanon is in question, however, the Other was artistic, free-spirited and probably the most humorous of the founders. In some canons, Eutenoyar and the Other were the same person, and in some Eutenoyar was the founder of the Patrexean Chapter.
lazuline
The Seal of Lazuline in Cerulean colors.
Lazuline, the founder of the Cerulean Chapter, has no counterpart in canon, but many of the members of New Gallifrey who have a spiritual connection to Gallifrey remember her or remember learning of her in history. Additionally, she exists within Na Galifreia, a Gallifreyan conlang project created by several Tumblr users, and was "created' as the founder of the Cerulean Chapter by two members of that project. The founder who has been most commonly seen as female, Lazuline was sophisticated, serious, caring about others and in many cases the first Gallifreyan Healer.
apeiron
The Seal of Apeiron in Dromeian colors.
Apeiron was the founder of the Dromeian Chapter, and is listed on the official Doctor Who wiki as possibly having been one of the founders of Time Lord society. As a member of the Lower Triad and a Dromeian, Apeiron was less concerned with politics and more concerned with the stability of Gallifreyan society. Not much is known about him. His name means "that which is boundless" in Greek.
pandak
The Seal of Pandak in Scendelesean colors.
Pandak was the founder of the Scendelesean Chapter, and canonically one of the founders of Time Lord society in Doctor Who, along with being president during the war against the vampires. As a member of the Lower Triad and a Scendelesean, Pandak was focused on stability and mathematics. Not much is known about them. Their name means "short" and/or "stout" in many languages.