"Nicolas Flamel is the only known maker of the Philosopher’s Stone!" -- Hermione Granger (PS13)
The most fabulous magic item of them all, the goal of alchemists and wizards for centuries. There was only one such stone known to be in existence, one created by Nicolas Flamel. The Philosopher’s Stone gives unlimited gold and immortality. Rather a nice payoff, but perhaps it isn’t as perfect as it seems, as Dumbledore says: “Humans tend to choose the things that are worst for them.” The Stone became the object of Voldemort’s desire in his quest for immortality, and it was only through the intervention of Harry and his friends that Voldemort didn’t obtain it from its hiding place in Hogwarts.
"‘Nicolas Flamel,’ she whispered dramatically, ‘is the only known maker of the Philosopher’s Stone!’" -- Hermione Granger (PS13)
Passage that Hermione Granger reads from:
The ancient study of alchemy is concerned with making the Philosopher’s Stone, a legendary substance with astonishing powers. The Stone will transform any metal into pure gold. It also produces the Elixir of Life, which will make the drinker immortal.
There have been many reports of the Philosopher’s Stone over the centuries, but the only Stone currently in existence belongs to Mr Nicolas Flamel, the noted alchemist and opera-lover. Mr Flamel, who celebrated his six hundred and sixty-fifth birthday last year, enjoys a quiet life in Devon with his wife, Perenelle (six hundred and fifty-eight). (PS13)
"'The dog must be guarding Flamel’s Philosopher’s Stone! I bet he asked Dumbledore to keep it safe for him, because they’re friends and he knew someone was after it. That’s why he wanted the Stone moved out of Gringotts!’" -- Hermione Granger (PS13)
"...Harry and Ron were still discussing what they’d do with a Philosopher’s Stone if they had one." (PS13)
"Could Snape possibly know they’d found out about the Philosopher’s Stone? Harry didn’t see how he could – yet he sometimes had the horrible feel- ing that Snape could read minds." (PS13)
"‘Oh, I thought we’d keep this private,’ said Snape, his voice icy. ‘Students aren’t supposed to know about the Philosopher’s Stone, after all.’" -- Severus Snape (PS13)
"‘So we were right, it is the Philosopher’s Stone, and Snape’s try- ing to force Quirrell to help him get it. He asked if he knew how to get past Fluffy – and he said something about Quirrell’s “hocus- pocus” – I reckon there are other things guarding the stone apart from Fluffy, loads of enchantments, probably, and Quirrell would have done some anti-Dark Arts spell which Snape needs to break through –’" -- Harry Potter (PS13)
"Hermione, however, had more on her mind than the Philosopher’s Stone. She had started drawing up revision time- tables and colour-coding all her notes." (PS14)
"‘Oh, we found out who he is ages ago,’ said Ron impressively. ‘And we know what that dog’s guarding, it’s a Philosopher’s St–’" -- Ron Weasley (PS14)
"‘We were wondering if you could tell us what’s guarding the Philosopher’s Stone apart from Fluffy.’" -- Harry Potter to Rubeus Hagrid (PS14)
"All the same, he’d have gambled twelve Philosopher’s Stones that Snape had just left the room, and from what Harry had just heard, Snape would be walking with a new spring in his step – Quirrell seemed to have given in at last." -- about Harry Potter (PS14)
"‘The Philosopher’s Stone! Of course – the Elixir of Life! But I don’t understand who –’" -- Harry Potter to Firenze (PS14)
"‘Look,’ said Harry, throwing caution to the winds, ‘Professor – it’s about the Philosopher’s Stone –’" -- Harry Potter to Minerva McGonagall (PS16)
"‘Get out of the way,’ he said. As Harry moved aside he felt the Philosopher’s Stone against his leg. Dare he make a break for it?" -- Quirinus Quirrell to Harry Potter (PS17)
“From what Dumbledore’s said, you’ve managed to get through stuff like this plenty of times. Broke your way through a series of obstacles guarding the Philosopher’s Stone in your first year, didn’t you?” -- Alastor "Mad Eye" Moody to Harry Potter (GF29)
“But my plan failed. I did not manage to steal the Philosopher’s Stone. I was not to be assured immortal life.” -- Lord Voldemort (GF33)
“There was no hope of stealing the Philosopher’s Stone anymore, for I knew that Dumbledore would have seen to it that it was destroyed." -- Lord Voldemort (GF33)
“'WHO SAVED THE PHILOSOPHER'S STONE? WHO GOT RID OF RIDDLE? WHO SAVED BOTH YOUR SKINS FROM THE DEMENTORS?'” -- Harry Potter (OP4)
“Bet it is!” said George. “That’s where he hid the Philosopher’s Stone!” -- George Weasley (OP6)
“Philosopher's,” hissed Hermione.” -- Hermione Granger to Neville Longbottom (OP16)
“'I’m three years older than you were when you fought You-Know-Who over the Philosopher’s Stone...'” -- Ginny Weasley to Harry Potter (OP33)
“Why did you stop the Dark Lord procuring the Philosopher's Stone?" -- Bellatrix Lestrange to Severus Snape (HBP2)
“I think you next wanted to know,” he pressed on, a little more loudly, for Bellatrix showed every sign of interrupting, “why I stood between the Dark Lord and the Philosopher’s Stone” -- Severus Snape to Bellatrix Lestrange (HBP2)
“Why couldn’t he make a Philosopher's Stone, or steal one, if he was so interested in immortality?” -- Harry Potter to Albus Dumbledore (HBP23)
“But there are several reasons why, I think, a Philosopher’s Stone would appeal less than Horcruxes to Lord Voldemort." -- Albus Dumbledore to Harry Potter (HBP23)
“Beedle probably took the idea from the Sorcerer’s Stone; you know, instead of a stone to make you immortal, a stone to reverse death.” -- Hermione Granger (DH21)
The title was changed because Scholastic thought that a child wouldn't buy a book with the word "philosopher" in the title.
"Philosopher" is from Old English, philosophe, Latin, philosophus, and Greek, philosophos, meaning one who speculates on the nature of things and truth" and "lover of wisdom." In Middle Ages, the word was tied to alchemy, which is why the stone is named the "Philosopher's Stone."