Known Parselmouths Ginny Weasley was able to speak Parseltongue while she was possessed by Tom Riddle's Diary, which enabled her to open the Chamber of Secrets.
In Harry Potter and the Half-Blood Prince, three more Parselmouths are introduced: Marvolo, Morfin and Merope Gaunt. We learn at the same time that Professor Dumbledore understands Parseltongue, and presumably can speak it, though he never does so in Harry's hearing.
The Heir of Slytherin turns out to be Ginny Weasley, who is being controlled via a magical diary that once belonged to Tom Riddle, AKA Voldemort.
Lord Voldemort lived inside those pages, and Ginny was eventually possessed as the Dark wizard began to absorb her strength, control her into opening the Chamber of Secrets, and nearly killed her. The event, though undeniably traumatic, was a pivotal point in Ginny's life.
Ginny WAS NOT the heir of Slytherin. It was Voldemort. Voldemort (or in this case, teen Riddle) instead took posession and control of Ginny via the diary (one of his horcruxes) in Chamber of Secrets.
In the Chamber itself, we see a large statue of a wizard, which Harry presumes is Salazar Slytherin. We also meet Tom Riddle, who is, as it turns out, the heir of Slytherin. Present only in spirit, he has all the same been controlling Ginny, and having her act as Slytherin's heir.
Andrea Deanisi as Wiglaf Sigurdsson, the Heir of Rowena Ravenclaw.
Through this dialogue, Tom grew stronger and ultimately poured a little of his soul into Ginny, manipulating her to kill Hagrid's roosters and open the Chamber of Secrets.
SHE'S A PROFICIENT AND POWERFUL WITCH
J.K. Rowling has stated one of the reasons Ginny is gifted is due to the fact she was a seventh child and the first female Weasley born in generations, which ties into the superstition of the seventh daughter of a seventh daughter.
Puffskeins come in many forms, from standard 'custard-colour' to the American Appaloosa, but best of all had to be Ginny Weasley's purple Pygmy Puff, a modified Puffskein bred by Fred and George. Wouldn't you love to have that little guy riding around on your shoulder?
Harry is the Heir of Gryffindor (though his powers have been bound by his father when he was a baby), Neville is the Heir of Hufflepuff, Meghan (OFC, daughter of Sirius) is the Heir of Ravenclaw. Harry/Ginny, Ron/Hermione, Remus/Tonks. Sixth year. After a rare magical illness Harry becomes outstandingly powerful.
Ginny Weasley was able to speak Parseltongue while she was possessed by Tom Riddle's Diary, which enabled her to open the Chamber of Secrets.
While it's true that Voldemort is a descendant of Salazar Slytherin, he is the “Heir of Slytherin” because he is a parselmouth and he figures out he needs to communicate with the basilisk to open the Chamber of Secrets. Tom Riddle, Jr simply appropriates the title “Heir of Slytherin” for himself.
An individual who can speak Parseltongue is known as a Parselmouth. It is a very uncommon skill, and is typically hereditary. Nearly all known Parselmouths are descended from Salazar Slytherin with Harry Potter being a notable exception.
His ability to speak Parseltongue is why the Slytherin emblem is a serpent. Merlin himself was sorted into Slytherin when he was at Hogwarts, and the young wizard went on to become one of the most famous wizards in history.
Ron spoke Parseltongue in Harry Potter and the Deathly Hallows to open the Chamber of Secrets. But before you dismiss this detail as ridiculous or overly convenient, consider that maybe it wasn't mere mimicry on Ron's part. It's worth delving into the logic behind Ron's surprise ability.
Ginny Weasley
The film adaptations of the books did Ginny Weasley wrong. The youngest Weasley child and only daughter wasn't just Harry Potter's love interest, she was an extremely capable witch who arguably had more power than her famous partner.
Ginny and the Bat Bogey Hex
Ginny Weasley's aptitude for the Bat Bogey Hex was impressive enough to earn her the admiration of no less a talent-spotter than Professor Slughorn.
Ginny's temper, along with her penchant for cruel bullying seemed to be celebrated by many of the series' characters and J.K. Rowling, herself.
However, Tom was in love with a Muggle woman named Cecilia and did not noticing Merope or her affections towards him. Determined to have Tom for herself, Merope was said to have given Tom a love potion to make him fall in love with her.
Cecilia was a young, pretty Muggle woman who seemed to have been romantically involved with Tom Riddle Senior prior to his marriage to Merope Gaunt.
The Chamber was in fact opened, approximately fifty years before the time of the Harry Potter series, by Tom Riddle (who later styled himself as Lord Voldemort).
Moaning Myrtle
Born in the late 1920s to Muggle parents, Myrtle Warren started her Hogwarts life in the early 1940s, where she was sorted into Ravenclaw. 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.
The Heir of Hufflepuff was none other than Cedric Diggory, who was well on his way to fulfilling the prophecy of the Heir of Hufflepuff when he was tragically murdered by Peter Pettigrew. Thus, the prophecy would remain unfulfilled forever.
She is perceptive
Ravenclaws are perceptive, and Luna noticed all kinds of things others didn't during her time at Hogwarts. There was that time she explained Ron in one sentence: 'He says very funny things sometimes, doesn't he?