Is the Doctor really this person?

Question

In the episode The Timeless Children (S12E10), it's stated that the Doctor

is the Timeless Child, a being who has always existed and can infinitely regenerate.

Is this a safe assumption?

Answer 1

The simple answer is we don't know for sure. Hopefully Season 13 will clarify it, but we do have enough to note what we do know.

Tons of Season 12 spoilers. Fair warning

Let's break down the arguments for and against

Against

• This information comes from The Master. Not exactly a sane version of him either
• The Master has been feeding visions to The Doctor. Anything she's envisioned is suspect
• The Timelord Matrix is missing a metric ton of information
• None of this has ever been mentioned before and it really shatters some of what we know about not just The Doctor, but the entirely of Who-dom. I mean, if this Tecteun did really make it so Timelords could regenerate, then a lot of previously canon Timelord history is flat out wrong.

For

• The Doctor herself confirmed the Ruth Doctor is really her, but there's no recollection. Given that she reappears in the Matrix to pep talk the current Doctor, it seems more likely she's the real deal. There's no other way to explain her and we don't know how the new chronology fits with what canon we do have on The Doctor
• The Doctor seems to have some of this innate knowledge being brought to the surface without The Master present
• This would help explain why The Doctor gets more than 12 regenerations

Answer 2

At this point in the story (the conclusion of season 12) it is not a "safe assumption", for at least four reasons:

The Master could be an 'unreliable narrator'

The Doctor has been told by The Master that she is/was the Timeless Child, but we don't know if that is correct. He may be lying, or even be mistaken.

All of the information relayed to The Doctor by The Master came from the Time Lord database known as The Matrix. We know from the same episode that parts of the Matrix have been deleted, and other parts of it have been encoded. The information about the Timeless Child ended with the Timeless Child being enrolled into The Division by their adopted parent (Tecteun) and we saw nothing within that data that linked the Timeless Child to The Doctor.

We also know from the earlier 6th Doctor serial The Trial of a Time Lord that The Matrix can be tampered with, as the Valeyard was able to completely change recorded events in order to falsify evidence. For all of these reasons, it is not yet possible to authoritatively assert where the story will go, as we can neither trust The Master, nor his source of information.

There is more evidence placing the 'Fugitive Doctor' in-between known regenerations than before the 'first' Doctor

The appearance of the 'Fugitive Doctor' (also referred to by some as the 'Ruth' Doctor), a previously unknown incarnation of The Doctor, has been taken by some to be the 'proof' that The Doctor is the Timeless Child because their existence is both evidence that (i) The Doctor has had their memory wiped and had a longer life than we previously knew about, and (ii) that The Doctor worked for The Division during that previously lost period. However, as the Matrix was missing the end of the Timeless Child's story and we do not yet know the beginning of the Fugitive Doctor's story, there is nothing definitely tying these together.

Among the pieces of evidence that currently places the Fugitive Doctor after the First Doctor are:

1. They call themselves 'The Doctor' - a name The Doctor remembers choosing for themselves.
2. Their TARDIS is disguised as a police box - we are told that the chameleon circuit of the Doctor's TARDIS became stuck that way whilst in their possession (or that it was faulty when the First Doctor stole it, according to The Name of The Doctor)

A popular fan-theory at the present time is that the Second Doctor, who we never saw regenerate, had their memory wiped by the Time Lords, was put to work in The Division (for an unspecified number of regenerations), and then had their mind wiped again and their regeneration cycle fixed before being returned to Earth.

There are some inconsistencies between the available account of the Timeless Child in the Matrix and the 'Brendan' allegory

Some of the information about the Timeless Child was not actually redacted from the Great Matrix but had a 'visual filter' put over it by Tecteun to prevent it from being recognised. It presented details of the Timeless Child's story as the story of a human foundling called Brendan who lived in Ireland. Among the details from this allegory that do not match up are:

1. Brendan was found by 2 adoptive parents - the Timeless Child was raised only by Tecteun.
2. Brendan was enrolled in the police force by his father and fell off a cliff in the line of duty - the Timeless Child fell off a cliff as a child and was enrolled in The Division later, as an adult.

A possible resolution to these conflicting details is that the Brendan allegory represents The Doctor, but not the Timeless Child. Both of them were put into the Division, and The Doctor became aware of The Timeless Child during this time. This may even be the reason why they were on the run as the Fugitive Doctor. This would also explain how, in The Ghost Monument, The Remnants saw 'The Timeless Child' buried in The Doctor's mind.

Even if The Timeless Child is The Doctor, we know nothing about their origin or abilities.

We learned that the child was found and is an unknown species. We don't know how many regenerations they can have, but we do know that the Time Lords developed their own regenerative abilities from this child, and they chose to restrict it to 12. I don't think we can assume that they "always existed", as we have seen that The Doctor grew to adulthood, so although the child's origins were unknown, she was still a child and must have had a beginning. The Doctor's assumption was that The Time Lords must have forced her to regenerate back to childhood if memories of her previous existence had been erased. It seems reasonable to assume that if they found a way to restrict their own regenerations to 12 that they could impose that limitation on the child (The Doctor) too.

Hopefully, many of these questions will be answered or confirmed in the following season. As many actors playing The Doctor have done so for 3 years/seasons, it seems plausible that the next season will complete a three-season story arc.

Answer 3

Disregarding the Master's commentary (see also the other answers), it is clear that we don't know who the Timeless Child turned into.
If we assume the information in the Matrix to be correct, the Child was found and experimented on and used to create the regeneration process for Time Lords. But a large part of the information in the Matrix is missing, and we never get to see anything beyond a certain point. Everything after that is just a guess.

So, my guess is that the Child is Rassilon, but yours is as good as mine.

Anyway, it's obvious that we, the viewers, are misled by the images we get to see. In Fugitive of the Judoon, Ruth says she's "the Doctor", she calls her time capsule a "TARDIS", and it looks like a police box. These three clues clearly date her as later than the Hartnell doctor - he was the one who stole the time capsule, had it renamed "TARDIS" (by Susan), and noticed that its chameleon circuitry was damaged so it always looked like a police box. And as a renegade, he got his name changed from his original one to "The Doctor".
So Ruth must have come after him, not before.

Yet in The Timeless Children, Ruth is explained as being one of the regenerations that came before the First Doctor. Ha, ha. We are being played for fools.