I was wikipeding the episode and saw his name in the cast and I was like wat
Right. I went and checked and it’s true. The credits in the episode itself claimed Rondo Haxton, but the BBC website says Gatiss. (Proof. Click the Credits bit.) I can’t stop laughing.
Apparently after Rondo Hatton, a B-movie actor who was quite a looker as a result of acromegaly.
Apparently it’s also a very obscure Sherlock Holmes reference, as this forum thread would suggest. Hatton played the Haxton creeper in The Pearl of Death, a Rathbone film from 1944.
The Mofftiss is being confusing again. I bet they’re having a laugh.
And now that I’ve given up laughing for linking, have a Tardis Wiki page as well.
(And also an afterthought: The Golem in Sherlock bears remarkable similarities. Great Game was penned by Gatiss, wasn’t it? Seems to be a running joke.)