Fred and George are friends of Harry Potter, members of the Order of the Phoenix, and founders of the joke shop Weasleys' Wizard Wheezes.

In Harry Potter and the Goblet of Fire, Fred and George begin selling their own jokes by owl order, under the name "Weasleys' Wizard Wheezes."

In Goblet of Fire, they try to encourage Harry and Ron to find dates to the Yule Ball by letting them see Fred ask Angelina Johnson.

They were also members of Dumbledore's Army, a group started by Harry, Ron, and Hermione to teach practical instruction in Defence Against the Dark Arts, which Umbridge had removed from that course's curriculum.

Later that year, they are banned from Quidditch and decide to abandon formal education; before leaving, though, they pay tribute to Dumbledore by waging a prank war against the dictatorial Dolores Umbridge.

It is stated by several characters, including Professor Flitwick and Hermione, that despite their poor grades, the Weasley twins are extremely proficient wizards, capable of sophisticated magic.

This is evidenced by the large number of inventions they have created and by Fred's ability to transform Ron's teddy bear into a spider even before he was old enough to attend Hogwarts.

In The Half-Blood Prince, Fred and George continue to run their very successful joke shop, Weasleys' Wizard Wheezes, out of Diagon Alley.

George loses one of his ears to Snape's Sectumsempra curse (which was aimed at a Death Eater's wand hand, but missed).

It is impossible for Fred and George to return to their shop in Diagon Alley to sell their products, so they begin to run another owl-order business out of their Auntie Muriel's house.

Before his death, Fred reconciles with his estranged brother Percy, who arrives at Hogwarts to participate in the fight and apologises to the family for not believing them.

Fred died with a smile frozen on his face, as moments before death he was laughing at Percy for making a rare joke.

However, as the twins explain to Hermione in Harry Potter and the Order of the Phoenix, they do avoid getting in serious trouble, pointing out that, despite all their rule-breaking, they have never been kicked out of school.

When Dumbledore is forced out of Hogwarts, they decide to cause real mayhem for the new headmistress, the hated Dolores Umbridge, something that they had always stopped short of before, for example by creating swamps in the corridors and setting off fireworks that multiply.

To date, Rowling has apologised for the deaths of Remus Lupin, Severus Snape, Dobby the House Elf and Sirius Black, along with Fred's.