Timeless Child's species

The 'Timeless Child's species' are a largely unknown species from another planet, universe or dimension. They are the Doctor's original species, as the Timeless Child, and are physiologically extremely similar to Time Lords, as the Doctor was able to spend their entire known life under the belief they were a Time Lord, with nobody being any the wiser.

However this species is differentiated from the Time Lords by at least one single factor; they naturally held the ability to regenerate into new bodies indefinitely. The Timeless Child, the only known member of this species, was found near a boundary to another reality or dimension from which they had come through.

After being brought to Gallifrey by the Shobogan Tecteun, the Timeless Child's biodata was used as a template to allow for regeneration in other Shobogans within the Citadel. Copying this ability allowed them to become Time Lords; with noting that a little bit of the Doctor had been inside him all along. Though unlike the Timeless Child's species, their copied version was limited to sets of twelve (though this appeared to be a choice, rather than a shortcoming). (TV: The Timeless Children)

Life cycle
When this species gets severely injured, their bodies will emit a huge amount of golden energy that may cause huge amounts of damage to the surrounding area.

When this happens, their appearances will change as well as their personalities. The Master theorised that this race could regenerate an infinite amount of times. (TV: The Timeless Children)