Hagrid told him he was a wizard.
for Dumbledore
Lily Luna Potter, Harry's daughter, would have grown up knowing because all her family would be magical. Lily Evans, Harry's mother, was told by Severus Snape and it was confirmed by her Hogwarts letter. Somebody would have come and explained it to her parents like Hagrid did with Harry (only they thought he knew).
Rubeus Hagrid.
The Hogwarts gamekeeper (also known as the Hogwarts groundskeeper) is a Wizard employed by Hogwarts School of Witchcraft and Wizardry to tend to and look after the grounds of the school, as well as the security of Hogwarts Castle. It is Rubeus Hagrid.
Hagrid is of mixed human and giant parentage, his mother is the giantess Fridwulfa and his father was a tiny wizard.
I would ask Hagrid if it is Wizard April Fools. (Even if it was July 31st)---- I would ask if this was a BIG joke or something. ---- Well, there aren't many things you can ask a giant if he tells you you are a wizard. You think there are many questions in your head but your just curious.----
Hagrid's Mother. She is a giant and had relations with a wizard but she then left him to care for Hagrid and had relations with another giant giving Hagrid a half brother called Grawp. In OOTP Hagrid says that he was told that she died years ago.
Hagrid told him he was a wizard.
Rubeus Hagrid was born on the 6th December 1928 to a giant and a wizard. His mother left when Hagrid was around three years old, leaving him to be raised by his father.
Hagrid is of mixed human and giant parentage, his mother is the giantess Fridwulfa and his father was a tiny wizard.
Among the many facts that Harry Potter learned from Rubeus Hagrid are that Harry is a wizard and that his parents were not killed in a car crash, but murdered by Lord Voldemort. Throughout his years at Hogwarts, Harry learns others things from Hagrid who becomes his Care of Magical Creatures professor for three years.
Harry Potter is told he is a wizard by Rubeus Hagrid, Keeper of Keys at Hogwarts in Chapter 2.
for Dumbledore
A half-giant named Hagrid breaks into a house where Harry and his aunt, uncle, and cousin are hiding. Hagrid gives Harry a smashed birthday cake, tells him he's a wizard, invites him to the wizard school, Hogwarts, gives Harry's cousin a pig's tail, and takes Harry away to get him ready for school.
Fridwulfa was his mum, don't think he mentions his dad...
The person who takes Harry from the Dursleys, was Hagrid.