According to a "secret history" unearthed by the Spy Master from the depths of the Matrix, the Shobogans were the original indigenous people of Gallifrey, who, after splicing the Timeless Child's regeneration-enabling DNA into their biodata and discovering time travel, became the Time Lords. (TV: The Timeless Children)
The term of "Shobogan", sometimes corrupted to "Shabooj'm", became used for people on the fringe of the Time Lord civilisation, with most Time Lords no longer applying it to themselves. (TV: The Deadly Assassin, PROSE: All-Consuming Fire, The Eight Doctors, etc.)
Biology
The Shobogans appeared externally identical to humans. As the Spy Master claimed to the Thirteenth Doctor, they gained the ability of regeneration from the Timeless Child, a member of an unidentified species. As a result, they became known as Time Lords. (TV: The Timeless Children)
History
Tecteun was one of the first inhabitants of Gallifrey to explore other planets. Via the Boundary, she discovered the Timeless Child on one such planet, and adopted her as her own. She later brought the child back with her to Gallifrey.
When Tecteun discovered the child's ability to regenerate, she experimented on several of their incarnations to discover the secret to this ability to the point where it became an obsession of hers to find out the mysteries of regeneration. Eventually she injected herself with the genes which had been spliced from the child. Upon doing so she immediately regenerated into a male incarnation. Tecteun later gave his people living in the Capitol this gene so that they would be able to regenerate and limited the regeneration cycle to twelve regenerations. This was to become the foundation of an elite society; they came to be known as Time Lords. (TV: The Timeless Children)
Notably, in other accounts, the Time Lords' ancestors were simply known as the Gallifreyans, and they had already long developed space travel when they discovered regeneration in very different circumstances. (PROSE: The Legacy of Gallifrey)