Merlin indeed existed in the Harry Potter universe and was sorted into Slytherin House during his time at Hogwarts. He might have even been taught by the founder Salazar Slytherin himself. Despite being taught by the anti-muggle wizard, Salazar Slytherin, Merlin believed that wizards should live peaceably among muggles, displayed by his work with King Arthur and his court. It was because of this attitude that Merlin created the Order of Merlin, which was an organization that promoted muggle rights and created laws to protect them from misuses of magic. Through time, the Order of Merlin became an award through the Ministry of Magic that was given to witches and wizards who performed a great act of bravery or contributed to the betterment of wizarding society in some way.
3. Nicholas Flamel Attended Beauxbatons Academy Of Magic
The famous inventor of the Philosopher's Stone didn't attend Hogwarts like so many other famous witches and wizards we have come to know though the Harry Potter series. Instead, he attended Beauxbatons Academy of Magic in France. It was here that he met his wife, Pernelle. After he reached fame for his Elixir of Life, he donated money to help fund the development of the school's castle and grounds, and a prominent fountain was then named after the couple.