What's the most ancient non-muggle event or person ever mentioned in the Harry Potter series? How far back in history do references go? I know that Merlin is mentioned... any further back?
Note that anyone mentioned as Video Game canon is from the Famous Wizard Chocolate Frog Cards from the games.
(Video Games canon) Goliath was (in HP universe) a Giant mercenary. David was born around c. 1040 BC (Wiki) so Goliath was born even earlier.
(Book and Movie canon) Sign at Ollivanders Wand Shop, in Diagon Alley; "Makers of Fine Wands since 382 B.C."
(Book canon - Fantastic Beasts) Harpo the Foul - the first wizard known to both create a Horcrux and hatch a Basilisk. He lived in Ancient Greece at unknown time (the Ancient Greek time period officially ends ~600AD); Basilisks in legend definitely precede 600AD by a large margin.
(Video Games canon) The following wizards were also from Ancient Greece, dates unknown:
Mopsus the seer
Falco Aesalon: was the first recorded Animagus.
Andros the Invincible: Alleged to have been the only known wizard to produce a Patronus the size of a giant.
Please note that these ALL precede Merlin, who was mentioned to have attended Hogwarts - sourced from Wikia, so not sure of canonicity.
Also, see the Timeline in HP Lexicon.
The oldest person mentioned by name is probably Circe, a witch who had lived near the Trojan War. The dates are uncertain, but it was probably near 1240 BC.
Circe is mentioned in Harry Potter and the Philosopher's Stone chapter 6, where she is one of the names to appear on the “Famous Witches and Wizards” cards of Chocolate Frogs.
For reference, here is the list of names from Chocolate Frog cards in that chapter: Albus Dumbledore, Agrippa, Ptolemy, Morgana, Hengist of Woodcroft, Alberic Grunnion, Circe, Paracelsus, Merlin, the druidess Cliodna.
Most of these wizards and witches are not invented by Rowling, they are instead real or mythical people who are supposed to have lived in the middle ages or ancient times. Circe is probably the one who lived the earliest: Circe is already mentioned in the Odyssey.
Dumbledore is the odd one out in the list: he is invented by the Harry Potter books and he was born in 1881. is probably the most recent wizard in that list. Chocolate Frog cards do eventually get an expansion set with contemporary wizards though, as Rowling tells in an interview that Harry and Ron will eventually get featured on them.
The books barely mention almost about these old wizards and witches other than their names, so there can be some doubt that all of them refers to the famous real world mythological figure. Some of them could turn out to be different wizards or witches with a similar name. As far as I can remember, besides Dumbledore, Paracelsus is the only name mentioned again in a later book (Phoenix ch. 14).
It seems likely that there were already wizards in ancient Egypt setting up curses in the pyramids, even though no specific person is named.
The evidence for this is found in Prisoner of Azkaban Chapter 1.
First, an article in the Daily Prophet:
A delighted Mr Weasley told the Daily Prophet, ‘We will be spending the gold on a summer holiday in Egypt, where our eldest son, Bill, works as a curse breaker for Gringotts Wizarding Bank.’
Harry scanned the moving photograph, and a grin spread across his face as he saw all nine of the Weasleys waving furiously at him, standing in front of a large pyramid.
Then Ron's letter to Harry.
It's brilliant here in Egypt. Bill's taken us round all the tombs and you wouldn't believe the curses those old Egyptian wizards put on them. Mum wouldn't let Ginny come in the last one. There were all these mutant skeletons in there, of Muggles who'd broken in and grown extra heads and stuff.
Finally Hermione's letter to Harry.
Did you see that picture of Ron and his family a week ago? I bet he's learning loads, I'm really jealous – the ancient Egyptian wizards were fascinating.
Those ancient Egyptian wizards likely predate even Circe. The pyramids we know of were built much before the Trojan war (although there could be later pyramids that those wizards have hidden from Muggles).