From the Story
Discovered in Book 2, Chapter 3, The Burrow
"Percy Weasley is the third Weasley child and a sixth-year Prefect at Hogwarts. Over the summer, the Weasley twins believe he has been acting very oddly - sending several letters and spending a lot of time shut in his room."
Discovered in Book 2, Chapter 4, At Flourish and Blotts
"Percy accidentally sits on Errol at breakfast. He too receives a letter from school.
Discovered in Book 2, Chapter 9, The Writing on the Wall
"When Harry, Ron and Hermione investigate the toilet near the attack on Mrs Norris, Percy tells them off for being in a girls’ bathroom."
Discovered in Book 2, Chapter 12, The Polyjuice Potion
Percy bumps into Harry and Ron, disguised as Vincent Crabbe and Gregory Goyle, when they are in the dungeons looking for the Slytherin Common Room.
Discovered in Book 3, Chapter 8, Flight of the Fat Lady
When Percy arrives at the corridor in Gryffindor Tower, he wonders why the students aren't entering the common room. He can't believe that everyone has managed to forget the password and tells the gathered students to let him through as he is Head Boy. When he sees the slashed portrait of the Fat Lady, he immediately asks for someone to fetch Professor Dumbledore.
Percy helps organise the students as they settle down in the Great Hall for the night. When Dumbledore returns to the Great Hall, Percy asks him if there is any sign of Black, and whether they have found the Fat Lady. He asks Dumbledore whether the Dementors had wanted to help search for Black, but is told that no Dementor will enter Hogwarts whilst Dumbledore is Headmaster. In the days after the attack on the Fat Lady Percy sticks very close to Harry, tailing him like a rather pompous guard dog.
Discovered in Book 3, Chapter 15, The Quidditch Final
Percy makes his way on to the pitch after the Gryffindor victory. He jumps up and down like a maniac, all dignity forgotten as he celebrates.
Discovered in Book 3, Chapter 16, Professor Trelawney's Prediction
"Percy is getting ready to sit his N.E.W.Ts (Nastily Exhausting Wizarding Tests). He needs top grades, as he hopes to enter the Ministry of Magic after Hogwarts."
Discovered in Book 4, Chapter 5, Weasleys' Wizard Wheezes
"Percy is working in his bedroom when Harry arrives at The Burrow. He is full of self-importance due to his new job in the Department of International Magical Co-operation at the Ministry of Magic; he is working on a report about standardising cauldron thickness, and is irritated that Ron doesn't take his work more seriously. He constantly complains that his family are making too much noise, pointing out that he is trying to work.
Ron tells Harry that Percy is obsessed with his work at the Ministry, and is always talking about his boss, Mr Crouch. At dinner, Percy tells his father all about his work. He hints to the rest of the table that his department is working on a top-secret project, a big event that they are organising right after the World Cup. According to Ron, he has been trying to get the family to ask what the event is ever since he started working at the Ministry, with little success."
Discovered in Book 4, Chapter 6, The Portkey
"Percy is allowed a lie-in on the morning of the Quidditch World Cup, as he is Apparating to the campsite with Bill and Charlie. George tells Harry that Percy only passed his Apparition test two weeks before, and has been Apparating downstairs every morning since, just to prove he can do it."
Discovered in Book 4, Chapter 7, Bagman and Crouch
"Percy arrives at the tents just after the group has started cooking lunch, accompanied by Charlie and Bill. He makes a point of mentioning loudly that they have just Apparated in, then settles down to eat with the rest of the group.
Despite his apparent disdain of Ludo Bagman, Percy is eager to be introduced to the Ministry wizard; he hurries forward, hand outstretched, to greet him. He discourages the twins from showing Bagman any of their inventions, and is stunned and disappointed when Bagman appears delighted by their fake wand. When the conversation turns to Barty Crouch, Percy's boss, he positively writhes with excitement, informing the group that Crouch speaks over two hundred languages. Percy sinks into some kind of half bow when Crouch arrives at their tents, and offers him a cup of tea. He looks embarrassed when Crouch refers to him as 'Weatherby', and busies himself with the kettle, looking very pink around the ears."
Discovered in Book 4, Chapter 8, The Quidditch World Cup
"Percy joins his family, Harry and Hermione in the Top Box for the Quidditch World Cup match. Percy jumps to his feet so often as people enter the Top Box he looks as though he is trying to sit on a hedgehog. When Cornelius Fudge arrives, Percy bows so low that his glasses fall off and shatter. He is hugely embarrassed after this and, after repairing the glasses with his wand, remains in his seat from then on. He throws jealous glances at Harry, who is greeted by Fudge like an old friend."
Discovered in Book 4, Chapter 10, Mayhem at the Ministry
"Percy is furious when he hears what Rita Skeeter has written about the events at the Quidditch World Cup, and thinks that she has got it in for the Ministry of Magic. He is irritated that she wrote an article the previous week saying that the Ministry were wasting their time quibbling about cauldron thickness, an issue he feels very strongly about.
Neither Percy nor his father are at home much over the week following the Quidditch World Cup; they both leave the house early before the rest of the family are awake, and return well after dinner time. Percy tells the family that it has been absolute uproar at the Ministry, and that he has been putting out fires all week: people keep sending Howlers which, as they aren't opened immediately, explode on his desk, leaving scorch marks. He has been dealing with complaints about the security at the World Cup, and from the people who were at the campsite who want compensation for their ruined property. Percy thinks that his father was unwise to make a public statement about the events without clearing it with his Head of Department first."
Discovered in Book 4, Chapter 17, The Four Champions
"Mr Crouch tells Dumbledore that Percy, whom Mr Crouch is still referring to as 'Weatherby', has been left in charge at the office whilst he is visiting Hogwarts. Crouch thinks that, if anything, Percy is a little over-enthusiastic about his work."
As Prefect, one of Percy's duties is welcoming newly sorted Gryffindors to their house. As such, the Gryffindor welcome message on Pottermore has been written by him.
"Congratulations! I’m Prefect Percy Weasley, and I’m delighted to welcome you to GRYFFINDOR HOUSE. Our emblem is the lion, the bravest of all creatures; our house colours are scarlet and gold, and our common room lies up in Gryffindor Tower.
"This is, quite simply, the best house at Hogwarts. It’s where the bravest and boldest end up – for instance: Albus Dumbledore! Yes, Dumbledore himself, the greatest wizard of our time, was a Gryffindor! If that’s not enough for you, I don’t know what is.
"I won’t keep you long, as all you need to do to find out more about your house is to follow Harry Potter and his friends as I lead them up to their dormitories. Enjoy your time at Hogwarts – but how could you fail to? You’ve become part of the best house in the school."