One important aspect of the Harry Potter series is the Sorting Ceremony, which decides which house the students will be placed in during their time at Hogwarts. While the series isn't short of Gryffindors and Slytherins, the other two houses are somewhat overlooked, especially in the movies.
Ravenclaws are known for their wit, intelligence and creativity. Their house mascot is an eagle and their Head of House is Professor Flitwick. While it is one of the lesser featured houses, some of the most beloved characters, like Luna Lovegood, were sorted into Ravenclaw.
Padma Patil
While she was in Gryffindor in the movies, Padma was sorted into Ravenclaw in the books. The change was likely to keep her in the same house as her twin sister, Parvati, as they usually appeared together in the movies.
In the fourth movie, Ron takes Padma to the Yule Ball and memorably refuses to dance with her, as he is too focused on his jealousy over Hermione. Along with her twin sister, she also joined Dumbledore's Army and is clearly prepared to revolt against Umbridge. Although Padma doesn't get much screen time in the movies, she clearly fights on the side of good and is a trusted ally for Harry.
Rowena Ravenclaw
Rowena was one of the four founders of Hogwarts, and while she is one of the many Harry Potter characters that are mentioned but never seen, her legacy plays an important part in the series. Rowena valued those students of intelligence and learning, hence the traits associated with her house.
Her heirloom, Ravenclaw’s Diadem, was stolen by her daughter and later defiled by Tom Riddle, who used the artifact as one of his Horcruxes. The famous ever-changing floor plan at Hogwarts is also said to have come from Rowena, which shows just how much she valued logic and puzzle-solving. Although she doesn't directly appear, Rowena is mentioned several times in the movies, including after the opening of The Chamber of Secrets and during the battle of Hogwarts, and she left an important legacy behind at the school.
The Grey Lady
The Grey lady is Ravenclaw's house ghost and is later revealed to be Helena Ravenclaw, Rowena’s daughter. Helena, unfortunately, revealed the location of Ravenclaw's diadem to Tom Riddle, something she felt guilty about for many years after.
The Grey Lady also shares a history with one of the other house ghosts, The Bloody Baron, who actually killed her in a fit of rage. In death, Helena seemed quite timid and serene and often frequented abandoned classrooms. In the second movie, the Grey Lady is shown reading a book in the Gryffindor common room, showing she still valued the values of her house, even in death.
Quirinus Quirrell
Quirrell was the Defence Against the Dark Arts teacher in Harry's first year and memorably served as a vessel for Voldemort. Due to his timid nature and nervousness, many of the students and other professors didn't take him seriously, which made him the perfect disguise for the Dark Lord.
Unlike most of the other antagonists in the series, Quirrell wasn't a Slytherin and actually belonged to Ravenclaw during his time at Hogwarts. Although it may seem strange for a Ravenclaw to be manipulated in such a way, this only proves further just how powerful and intimidating Voldemort really was. As Quirrell had taught at Hogwarts previously as the Muggle Studies Professor, he probably wasn't always evil and most likely became corrupted by his quest for greatness, which is one of the most common weaknesses for Ravenclaws.
Gilderoy Lockhart
Lockhart took over from Quirrell as Defence Against the Dark Arts Professor and was also a Ravenclaw. Although he wasn't one of the most powerful Potterverse villains, he was certainly villainous. He was shown to be highly intelligent, using wit and charm in order to deceive his fans -- not that he ever fooled Harry or Ron.
Lockhart is also shown to be very proficient at memory charms, which he used on many successful Wizards in order to steal their accomplishments. Ironically, one of Lockhart's memory charms backfired when he threatened Ron and he was left as a dim-witted and feeble man, but he is still one of the most interesting characters from The Wizarding World.
Garrick Ollivander
Ollivander is a recognizable figure within the Wizarding World as he supplies most British Wizards and Witches with their wands. In a memorable scene from the first movie, he helps Harry to find his wand and explains its connection to Voldemort’s.
Ollivander reappears later on in the series when he is held prisoner at Malfoy Manor. Later, he explains wand-lore to Harry and the audience, and also the true significance of the Elder Wand. Ollivander's deep knowledge and understanding of wand lore makes him one of the wisest characters in the series, so it's unsurprising that he is a Ravenclaw.
Sybill Trelawney
Many Ravenclaws have unique and eccentric personalities and none more so than Trelawny. Although she teaches Divination at Hogwarts, the character is often ridiculed and regarded as a fraud.
However, despite her poor interpretation skills, Trelawney did appear to be a genuine seer. Her prophecy regarding Harry and Voldemort and their eventual fates was pivotal to the series and played a large role in the fifth movie. The way in which Trelawney interprets her own visions may be nonsense, but she does have strong and powerful abilities.
Moaning Myrtle
Moaning Myrtle may be a ghost haunting the girls' bathroom when fans first meet her, but she was once a Ravenclaw student at Hogwarts. Myrtle’s death is an important plot point, and despite her hilariously melodramatic nature, she did help Harry to uncover the truth about The Chamber of Secrets.
Most of her scenes do involve her wailing or cooing over Harry, but there are some occasions when she shows her intelligence. In the fourth movie, it is Myrtle who notices Polyjuice potion in the drains, and she also suggests that Harry puts the Golden Egg under the water in the prefects' bathroom. While Moaning Myrtle is mostly used for comic relief, her history is a key part of the series and she is one of the most memorable supporting characters.
Filius Flitwick
Professor Flitwick is the Charms professor at Hogwarts and also the head of Ravenclaw. In the movies, he is also shown to have a strong affiliation with music, which is fitting considering the creativity that many Ravenclaws possess.
Flitwick is arguably the most underrated teacher at Hogwarts and probably most memorable for teaching Harry and his classmates the levitating charm, Wingardium Leviosa. He clearly cared deeply about his students and his position at Hogwarts, as he is seen secretly celebrating when Umbridge is driven out by the Weasley twins. In the books, Flitwick is also known to be a skilled duelist and he defeats a number of dark Wizards in combat.
Luna Lovegood
Although Luna isn't introduced until the fifth movie, she is one of the most beloved characters in the Harry Potter series. Luna is often bullied and insulted for her individuality, but she never lets this affect her or alter who she is. Right from the off, she is loyal to Harry and eager to join Dumbledore's army and fight alongside him.
Luna Lovegood is one of the most eccentric characters in the Harry Potter universe, but despite her whimsical nature, she is shown to be extremely wise and thoughtful and appears to see things much deeper than the average person. Luna plays a key role in Harry finding Ravenclaw's diadem, which eventually helps him to defeat Voldemort. She is one of his best friends and strongest allies.