Appearing as the tenth doctor in the hit series "Dr. Who" or more recently as the Purple Man in the Netflix original "Jessica Jones," Tennant had a brief role in "Harry Potter and the Goblet of Fire" as Bartemius “Barty” Crouch Junior.
We can't blame you for missing him since he does play Griphook the Goblin in the first film, who meets his demise by Lord Voldemort after betraying Harry. Best known for his role as mini-me in the "Austin Powers" films, Troyer has made appearances in a number of films and TV shows since.
Still up and coming in his career, Luke is now well known for playing Magnitude on the NBC series "Community," but as a younger lad he played Lee Jordan in the first two films, commentating on Quidditch games and getting into hijinks with Fred and George Weasley.
This "How To Get Away With Murder" actor actually had a sizable role in the "Harry Potter" franchise, appearing in five films as Dean Thomas. Part of Harry's extended group of friends in Gryffindor, he was also an excellent Quidditch player.
Now dancing up a storm on "Dancing with the Stars," this pro actually had an uncredited role as a student at Hogwarts in the first film. His time on screen was very brief though, as you can briefly see him at the sorting hat with grungy red hair, braces and in a Hufflepuff outfit.
The popular franchise found the perfect role for the Monty Python legend as Nearly Headless Nick, the ghost that wandered about Gryffindor Tower, always more than happy to help those who've lost their way.
Also an uncredited Hogwarts student in the first film, Hough attended the same performing arts school as Mark Ballas and apparently all the students there were cast as extras. In House Ravenclaw, Hough liked to ham it up for the camera. He is an Emmy award winning dancing pro on "Dancing With The Stars" along with Ballas now.
Like her brother Derek and co-worker Mark Ballas, the "Dancing with the Stars" pro and actress also attended the performing arts school and thus got a part as an extra. She later revealed she had a huge crush on Daniel Radcliffe, and even wrote him a love note and bought him a beanie baby for Valentine's Day. She never heard back from him though.
Creeping everyone out as the 16-year-old Tom Riddle in "Harry Potter and the Half-Blood Prince," Dillane has just started making a name for himself in Hollywood, appearing in "Fear the Walking Dead" and "In the Heart of the Sea."
The Scottish actress best known for her roles in "Trainspotting" and "Bridget Jones's Diary" appeared in the second Potter film as Moaning Myrtle, whom you could find hanging around the first-floor girl's bathroom at Hogwarts.
As the quite handsome Tom Marvolo Riddle in "Chamber of Secrets," Coulson has been picking up roles here and there, such as in "Gossip Girl," "The Good Wife" and "Nurse Jackie."
This famous British actress from the '60s has won a number of awards including a Golden Globe and Oscar for Best Actress. She also appeared in "Harry Potter and the Prisoner of Azkaban" as Madam Rosmerta, the landlady of the Three Broomsticks pub in Hogsmeade.
Better known for the other famous series "Twilight," Pattinson actually had the part of Cedric Diggory in two "Harry Potter" films, a Triwizard Champion who unfortunately met his demise at Lord Voldemort’s orders.
The French actress does productions in both the US and her native France, with her most notable role in America being Eva Coupeau on "Gossip Girl." Poésy appeared in three Potter films as Fleur Delacour, who would eventually marry Bill Weasley.
The lead guitarist and keyboardist for the alt rock band Radiohead played Kirley Duke, the lead guitarist of the band know as Weird Sisters in the books, but due to a lawsuit was unnamed in "Harry Potter and the Goblet of Fire." Radiohead drummer Phil Selway was also in the band.
Now the wildling Osha who helps Bran in "Game of Thrones," Tena appeared in four "Harry Potter" films as Nymphadora Tonks, better known as just Tonks, the half-witch with the awesome hair.
The gorgeous eye candy in "Pitch Perfect" and soon-to-be Sam Tarly's brother in "Game of Thrones" played Cormac McLaggen in the last three films. He may have been a bit cocky, but come on, have you seen his abs?!
With a recurring roles in "Falling Skies" and later as Nora in "The Vampire Diaries," a younger Byrne played Malfoy's girlfriend Pansy Parkinson, who wasn't the kindest to Harry Potter.
Now best known as Catelyn Stark on the hit HBO show "Game of Thrones," Fairley played another important mother, that of Hermione's — yep, she was Mrs. Granger in the "Harry Potter" movies.
Appearing in such hits as the "Twilight" saga and "The Mortal Instrument," Bower played a young Gellert Grindelwald in "Harry Potter and the Deathly Hallows: Part 1," where a fallout out with Dumbledore eventually leads to the legendary duel.
This "True Blood" star made an appearance in numerous Potter films as Harry's aunt Petunia Dursley.
The former frontman of the British rock band Stone Roses accepted an uncredited part as a man reading "A Brief History of Time" in the Leaky Cauldron since his sons were such big fans of the series. He appeared in "Harry Potter and the Prisoner of Azkaban."