In the Series 3 two-parter "Human Nature" and "The Family of Blood", the Doctor uses something called a chameleon arch to make himself human. In the Series 3 finale, a similar device is used by the Master, again to make himself human.

But Time Lords look human anyway, so the only thing it needed to do in these cases was to rearrange their internal metabolism a bit; their outer appearance was identical to their Time Lord form. Can the chameleon arch do more than this? Could it make a Time Lord look like an Ood, or a Sontaran, or a Dalek? How much can it change their bodies?

I've probably seen all the on-screen appearances of the chameleon arch (unless it was a device recycled from Old Who?), but DW canon is so massive and multi-levelled that there may well be more information out there in some novel or comic or audiobook or goodness knows what.

What capabilities or limitations do we know the chameleon arch to have?

  • 1
    About the ood : we have already seen a transformation human to Odd, though not with the Chameleon arc
    – Edelk
    Sep 1, 2017 at 13:54
  • 2
    I don't know that it's ever explored, but I believe the Arch changes them to a cellular level, including rewriting their DNA. Given that instead of the human Double Helix, Time Lords have a Quadruple-helix (with one strand only visible to temporally aligned scanning) this is a pretty significant change, and fairly essential if he wants to pass as actually human in any even slightly advanced society. I suspect changes to any other species that share primarily human style DNA is trivial, but hasn't been explored.
    – K-H-W
    Sep 1, 2017 at 14:27
  • Given that we saw Romana simply voluntarily regenerate into various non-human forms, I would guess the Arch can do at least that much, but I don't think it's ever been explored, so I don't think we really have much data on it's limitations; just what we've seen / heard it do.
    – K-H-W
    Sep 1, 2017 at 14:30
  • It's not from the original run of the series, by the way. Chameleon circuit, yes; chameleon arch, no.
    – RDFozz
    Sep 1, 2017 at 20:23
  • @Edelk Yep, I even posted a question about that before.
    – Rand al'Thor
    Sep 2, 2017 at 11:31

1 Answer 1


The Chameleon Arch is known to be able to change the outward appearance, at least where physical age is concerned. The Master used a chameleon arch to change his appearance and escape the Time War. This is how the 10th Doctor found him as Professor Yana carrying a biodata module in the form of a pocket-watch identical to the one that The Doctor carried from the chameleon arch on his TARDIS. Professor Yana, the Master revealed that he had been found "an orphan in the storm. I was a naked child found on the coast of the Silver Devastation".

Big Finish audio dramas have established that it was The Master as portrayed by Derek Jacobi who fought in the Time War. The Chameleon Arch, therefore, was capable of turning the adult Master into the form of an infant, but evidently, he must have retained his genetics that affected his outward appearance given that he then grew into the identically-looking Professor Yana.

This is in line with the entry for The Master on Tardis Data Core which culls from all sources considered canonical including Big Finish. It suggests that The Master had the body of a child during the Time War (after being resurrected by the Time Lords to fight), but later regenerated into an older body in order to manipulate events in the war. It was after this that he used the Chameleon Arch to become an infant again. For the Doctor to not recognise him in the form of Professor Yana, he must not have engaged with him after the regeneration mentioned above.

  • Good find, but there's another possibility: the human Master might have been implanted with human memories. Presumably John Smith also remembered being a child in England, although he never was. (A less likely possibility is that the Master was lying - less likely because at that point his mind was still that of gentle Professor Yana.)
    – Rand al'Thor
    Apr 4, 2019 at 13:53
  • About the Doctor recognising him ... who knows how many regenerations the Master might have gone through between when the Doctor last saw him and when he used the watch? The Master seems to have a different face each time he crops up. And opening the watch didn't change his face back to anything the Doctor recognised: he still looked the same (before being shot and regenerating).
    – Rand al'Thor
    Apr 4, 2019 at 13:54
  • @Randal'Thor I did a bit more reading as I'm only really a completist on the TV show. It seems that the Chameleon Arch only changed the Master's apparent age, but not the genetics that would dictate his outward appearance. I have updated my answer.
    – Astralbee
    Apr 5, 2019 at 10:04

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