Hogwarts houses are a hallmark of the Harry Potter franchise. Gryffindors are as brave as lions, Slytherins are sly like snakes, Hufflepuffs are loyal like the humble badger and Ravenclaws value intelligence like eagles. While these fundamental traits are accurately prescribed to most, many key characters were sorted into the wrong houses during their time at Hogwarts.
The Sorting Hat is responsible for tapping into the minds of every student to see which house accurately captures their character. Although the Sorting Hat refuses to admit to its mistakes, these Hogwarts students did not live up to their Hogwarts houses and deserve to be rehomed. In fact, J.K. Rowling's world-building could have paid off better if these characters were shuffled around to showcase the diverse houses.
Harry Potter
The Boy Who Lived himself is in the wrong house. While there is no question that Harry is brave like a Gryffindor, there is also no question that Harry's most defining factors are his loyalty and sense of justice. In fact, his courageous acts are typically fuelled by his righteousness, such as rescuing Sirius Black when he discovers the truth about him. These qualities would make Harry the epitome of a hard-working Hufflepuff. Since the Sorting Hat was able to see traits from all the houses in Harry and was conflicted in his placement, the Hufflepuff house that takes all stragglers would be the logical fit.
Hermione Granger
If there's one thing classmates and professors of Hogwarts know about Hermione Granger, it's that she is the "brightest witch of her age." Routinely proved to be the most logical one of the titular trio between herself, Harry, and Ron Weasley, it is surprising Hermione was sorted into Gryffindor rather than Ravenclaw, the house of intellect and logic. Most adept at magic and book-smarts, Hermione uses her encyclopedic knowledge of magic and the wizarding world as her main superpower in the defeat of Voldemort and never strays from her plans. This devotion to information as power is the exact reason why Hermione should have been a representative of Ravenclaw.
Cedric Diggory
Cedric Diggory, played by Robert Pattinson in the films, is most known for his last stand of bravery in the Triwizard Tournament. As Harry is a Hufflepuff pushed to bravery while being rooted in justice, this Hufflepuff was loyal and fairminded, but his courage and chivalry are what rose to the top. Standing up to authority figures for a quidditch rematch and confronting Peter Pettigrew before his untimely death demonstrates his admirable bravery suited to the lions of Gryffindor.
Peter Pettigrew
Peter "Wormtail" Pettigrew is known as the man who murdered Cedric Diggory and Voldemort's most humble (and pitiful) servant. Although he once bravely joined the Order of the Phoenix, Peter quickly became one of the most cowardly characters in the series and cowered at the pressure of Voldemort's power. Peter not only became a spy within the Order's ranks but sold out his best friends (James and Lily Potter) to their deaths and let his other best friend (Sirius Black) take the blame. It is clear that Peter does not deserve the valiance that comes with being sorted into Gryffindor. His cunning and resourcefulness demonstrated by a flexible allegiance to power mean that Peter would have been more accurately sorted into Slytherin like the rest of the Death Eaters.
Gilderoy Lockhart
This wizarding celebrity, who stole the works of his fellow wizards to pass off as his own before wiping their memories, was sorted into house Ravenclaw. While it does take a certain degree of intellect to devise plans of intellectual property theft, Gilderoy Lockhart is not a worthy member of the cleverest house at Hogwarts since his academic accomplishments were not his own. His craftiness, arrogance and willingness to do anything for success make Gilderoy a better candidate for Slytherin.
Severus Snape
A prominent member of Slytherin house, Severus Snape was absolutely ambitious and clever. However, Snape was, above all, a lionhearted hero. The character demonstrates not all bravery is boisterous as he quietly sacrificed himself on numerous occasions for those he cared about, like Albus Dumbledore and Lily Potter. Snape embraced every challenge headfirst and feared no consequences, such as looking after Draco despite a deadly Unbreakable Vow. In spite of his cold exterior, Snape exhibited the valor of Gryffindor's house until his altruistic death.
Every character has dualities, like Zuko from Avatar, the Last Airbender, so there can easily be overlap in Hogwarts houses characters embody. However, the most defining traits of these characters and their actions outside of Hogwarts' walls prove that the Sorting Hat has definitely made some mistakes in its sapient life.