Yet they didn't just come with the building – well, not all of them anyway. Before they were ghosts, they were people – people with lives that were interesting, dramatic and sometimes gruesome. Here are some of the lesser-known stories of Hogwarts' spookiest squatters…
Nearly Headless Nick
After Hogwarts Nick found himself as a wizard at the royal court, who also knighted him. He was friendly with Muggles, including a lady-in-waiting from the court, Lady Grieve, who would ultimately be the cause of his doom.
The story goes that Nick met Grieve while strolling in the park, and – being the friendly chap he was/is – insisted that he could fix her crooked teeth with magic. But the spell backfired, and she instead started to grow a tusk. Nick was then arrested and sentenced to death – a botched beheading that, because of a dull axe, took 45 hacks to kill him, but still didn't sever his head from his body. Hence the nickname Nearly Headless Nick.
She had no friends, and was bullied relentlessly because of her glasses and acne. But she would soon have all of eternity to get her own back.
Myrtle’s transition from lonely student to eccentric ghost was thanks to the Chamber of Secrets. Having been teased by fellow student Olive Hornby, Myrtle ran into the first-floor girls' toilets and began sobbing in one of its stalls. It's here that she ran into Voldemort himself, Tom Riddle, who she overheard speaking Parseltongue in order to open the Chamber, which was hidden behind the sinks.
Thinking that Riddle was intruding in the girls' bathroom, she opened the stall door to tell him off – only to be confronted with the Chamber of Secrets' Basilisk, whose eyes killed her instantly. Her body was later found by Hornby, whose discovery would haunt her – both figuratively and literally. For Myrtle returned as a ghost and immediately started to torment Hornby. After a complaint to the Ministry of Magic, Myrtle was consigned to the bathroom forever.
A noble life for a noble man, but the Fat Friar's kindness was to be his undoing. For his fellow clergy grew suspicious at his ability to cure the pox with nothing but a stick, and he was soon executed. His penchant for pulling rabbits out of the communion wine probably didn't help either.
The Grey Lady
Helena's relationship with her mother was complex. An ambitious witch in the shadow of a brilliant one, Helena envied her mother's status and wisdom – which was enhanced by her enchanted diadem.
A few years into her magical education, she betrayed her mother by stealing the diadem – believing it could make her powerful – and running away from Hogwarts. The betrayal embarrassed Rowena, who told no one that the diadem was missing. On her death bed, however, she did send a young man to find Helena, so she could see her daughter for one last time. That young man tracked her down to a forest in Albania, and what happened next would be her downfall…
The Bloody Baron
Not much is known about the Baron beyond his involvement with Helena, but it's clear that he was a hot-tempered young man.
When Helena ran away with her mother's diadem, the Baron was the young man asked to track her down – which he did, to a forest in Albania. With her cornered, the Baron pleaded with Helena to come back with him, but – in her own words – became 'furious at my refusal, jealous of my freedom' and stabbed her to death.
Rightly horrified at what he had done, he then used the same knife to kill himself – sentencing himself to an eternity of penance, soaked in Helena's blood.