Who did the Anti-apparition Enchantment on Hogwarts?

Question

You can't apparate inside/to/from Hogwarts if you aren't headmaster (or, maybe applicable only to Dumbledore).

Who did that security spell to Hogwarts? Was that Dumbledore or founders of the school or someone else?

Answer 1

The four founders did it

J.K. Rowling's Pottermore entry about the Hogwarts Express says (emphasis added):

[...] Hogwarts students used to arrive at school in any manner that caught their fancy. Some rode broomsticks (a difficult feat when carrying trunks and pets); others commandeered enchanted carts and, later, carriages; some attempted to Apparate (often with disastrous effects, as the castle and grounds have always been protected with Anti-Apparition Charms), others rode a variety of magical creatures. [...]
_{(source: Pottermore)}

So, these magical countermeasures have been in effect since the school founding; we are not told who exactly performed them, but I think we can safely infer that the four founders originally did it.

Do the enchantments need periodic maintenance by the school staff? I don't think so, as we know of other magical feats dating back to the founders' time and still working: the Sorting Hat (belonged to Godric Gryffindor and enchanted by the four founders) and the Chamber of Secrets (enchanted by Salazar Slytherin alone).

"As you may know, it is usually impossible to Apparate or Disapparate within Hogwarts. The Headmaster has lifted this enchantment, purely within the Great Hall, for one hour, so as to enable you to practise. May I emphasise that you will not be able to Apparate outside the walls of this Hall, and that you would be unwise to try."
_{(Harry Potter and the Half-Blood Prince, chapter 18 - Birthday Surprises)}

Arguably, the Anti-Apparition Charms shielding Hogwarts were not ordinary magic, as it takes Dumbledore to lift it temporarily, partially (as it does not allow Apparition from / to the outer world, but only within the Hall itself) and in a small area.

In the books, even Dumbledore needs to exit Hogwarts grounds before Disapparating, and must Apparate outside them.

Answer 2

I'm pretty sure there is no canon information about this. We also don't really know whether spells fade over time or not, so we can't even assume that "whoever cast the original spell, Dumbledore is the one maintaining it" or anything like that. That being said, in HBP, the spell is partially lifted, and Twycross says "The Headmaster has lifted this enchantment" so at least we know that he is now in charge of it. And we do know that the spell is old: in PoA, chapter 9, when everyone has to sleep in the Great Hall because Sirius Black got in, someone suggests he might have Apparated in. Hermione replies "Honestly, am I the only person who's even bothered to read Hogwarts: a History?" [...] "There are all sorts of enchantments on it, to stop people entering by stealth. You can't just Apparate in here." This suggests that the anti-Apparition enchantment is old enough to be part of history. However, we don't know if it dates back to the Founders Era or later.