If some of the key characters in the hit HBO TV series “Game of Thrones” looked familiar to fans, there is a simple reason for that. Some of these “GoT” actors have played small but prominent roles in the “Harry Potter” movie series. Here are 5 “GoT” actors who played an important role in the "HP" film series.

Michelle Fairley: Catelyn Stark and Hermione’s mother

Catelyn Stark has one of the saddest stories in the whole “Game of Thrones” TV series.

If there is a symbol for a tragedy in the whole series, Fairley’s portrayal of Catelyn Stark should be strongly considered as its symbol.

Catelyn and Ned Stark have 5 children, Robb, Sansa, Arya, Bran, and Rickon. Ned Stark was beheaded by the order of King Joffrey Baratheon. Robb Stark, firstborn and eventual King of the North, was betrayed and killed by the same people who she considered an ally.

Sansa was abused, constantly humiliated, and considered a play thing by Joffrey Baratheon, married to the dwarf Tyrion Lannister. Bran ended up being crippled after being pushed by Jaimie Lannister off a tower window.

Rickon caught a Ramsey Bolton arrow in the back trying to get to Jon Snow. Arya was forced to learn how to become an assassin, suffering along the way.

Catelyn Stark appeared in 25 episodes spread throughout seasons 1, 2 and 3. She was first seen in “Game of Thrones” season 1 episode 1 and was killed in season 3 episode 9.

Meanwhile, Fairley played Hermoine Granger’s mother in “Harry Potter and the Deathly Hollows: Part 1.” The screen time was just a short one, and the role was fairly small for an actress of her stature, but given that she portrayed the role of the mother of one of the main protagonists in the movie series, her character makes her an important part of the “Harry Potter” movie series.

Ciaran Hinds: Mance Rayder, the King Beyond the Wall, and Aberforth Dumbledore

Mance Rayder is played by Ciaran Hinds. Rayder, the leader of the Free Folk, used to be a ranger of the Night’s Watch. He left the company of the men in black and joined the wildings, eventually unifying all the Free Folk tribes and earning his title as The King Beyond the Wall.

Rayder’s Free Folk army was caught by surprise and eventually defeated by Stannis Baratheon. Although Rayder surrendered, he refused to bend the knee for Stannis since the Free Folk don’t recognize Stannis as a King. He was saved from immediate death by Jon Snow who convinced Stannis to spare the King Beyond the Wall.

Mance Rayder was eventually burned alive after refusing to acknowledge Stannis as his King and refusing to lend the Free Folk army in his fight against Roose Bolton.

However, Snow, seeing the agony of the burning Rayder, shot the former man of the Night’s Watch in the heart with an arrow, killing him.

Ciaran Hinds appeared in 5 episodes of “Game of Thrones” and was first seen in season 3 episode 5. Jon Snow ended his participation in “GoT” in season 5 episode 1.

Hinds played the character of Aberforth Dumbledore in “Harry Potter and the Deathly Hollows: Part 2.” He has a slightly longer screen time than Michelle Fairley but played a crucial role in the movie. His bar served as a gateway inside Hogwarts School of Witchcraft and Wizardry, and Aberforth aided the member of Dumbledore’s Army in various times since Lord Voldemort’s return.

However, Aberforth Dumbledore played a more prominent role in the "Harry Potter" book series.

Aberforth intervened in a wizarding duel between his brother Albus, the famed Hogwarts Headmaster, and the Dark Wizard Gellert Grindelwald. In the ensuing fight, the Dumbledore brothers lost their only sister Ariana. Aberforth became estranged with Albus after that event.

Ciaran Hinds will next appear in the highly anticipated DCEU movie “Justice League” as Steppenwolf.

Natalia Tena: the wildling Osha and Nymphadora Tonks

The last time “Game of Thrones” followers saw the wilding Osha, the sadistic bastard Ramsey Bolton stuck a knife in her neck, killing her in dramatic fashion. While her death is a not as significant an event as it should have been, considering the things she went through and the things she did to protect young Bran and Rickon Stark, Osha’s death follows the unpredictable fatalities in the hit TV show.

Osha first appeared in “Game of Thrones” season 1 episode 6 trying to kidnap the crippled Bran Stark and was last seen attempting to kill Ramsey Bolton in season 6 episode 4. All in all, Natalia Tena appeared in 16 episodes spread between seasons 1, 2, 3, and 6.

While her mission was futile and ultimately ended in her death on “Game of Thrones,” her character in the “Harry Potter” movie series has deeper origins in the book version. Tena played the clumsy Auror Nymphadora Tonks (don’t call her Nymphadora, though) and first appeared as part of Harry Potter’s escort in “Harry Potter and the Order of the Phoenix.”

Tonks eventually marries Remus Lupin, one of Harry’s teachers and one of James Potter’s (Harry’s father) best friends.

Tonks and Lupin named Harry as the godfather of their child, Teddy Remus Lupin. Tena and Lupin both died during the massive Battle of Hogwarts scenes in “Harry Potter and the Deathly Hallows: Part 2.”

Tena also played the role of Tonks in “Harry Potter and the Half-Blood Prince” and “Harry Potter and the Deathly Hollows: Part 1.”

David Bradley: Lord Walder Frey and the Squibb Argus Filch

David Bradley played the role of Walder Frey, Lord of the Crossing, Lord of Riverrun, Lord Paramount of the Trident, and head of the House Frey. He was considered an ally of the House of Stark until he made a deal with Tywin Lannister to slaughter King Robb Stark, Queen Talisa (allegedly pregnant), Catelyn Stark, and the rest of their entourage.

David Bradley appeared in only 5 episodes in “Game of Thrones,” but his character’s impact is enormous since he stopped, in essence, the Northmen’s offensive against King’s Landing. Bradley was first introduced in season 1 episode 9 and was killed and mutilated by the vengeful Arya Stark in season 6 episode 10.

Bradley played the Squibb Argus Filch in the “Harry Potter” movie series, appearing in all 8 films. Filch is the resident caretaker of Hogwarts School of Witchcraft and Wizardry and one of the most ironic subjects in the “HP” movie series since Filch is known to hate students studying magic. But of course, his angst is probably borne out of his inability to use magic even if his parents are magical people.

Filch provided comic relief to the whole series as he is considered the exact opposite of half-blood wizards.

Jim Broadbent: Archmaester Eborse and Professor Horace Slughorn

Jim Broadbent started playing the role of Archmaester Ebrose in “Game of Thrones” season 7 episode 1. The title Archmaester is reserved only for the highest-ranking members of Order of Maesters. Samwell Tarly, a member of Night’s Watch, was on a mission in the Citadel to find a weapon against the White Walkers. He came to the attention of Ebrose especially after the former apparently cured Sir Jorah Mormont’s Greyscale.

Jim Broadbent first played the role character Professor Horace Slughorn in “Harry Potter and the Half-Blood Prince.” Slughorn is a Potion’s teacher at Hogwarts and was tricked by Tom Riddle into revealing the dark power of the Horcruxes.

Tom Riddle eventually became Lord Voldemort, arguably the strongest Dark Wizard in history.

What’s next for 'Game of Thrones' and 'Harry Potter'?

The next movie in the “Harry Potter” movie franchise is a sequel to the smash hit “Fantastic Beast and Where to Find Them.” The “Fantastic Beast and Where to Find Them” sequel is tentatively scheduled for release on November 16, 2018. It stars Johnny Depp, Eddie Redmaybem, Ezra Miller, Alison Sudol, and Zoe Kravitz. The movie is directed by David Yates and based on the screenplay of "Harry Potter" author J.K. Rowling.

Meanwhile “Game of Thrones” enters the climax of season 7. Season 7 episode 4 is set to be aired on August 6. “GoT” season 7 only has only 7 episodes in total. Season 8, the final season of the tv series, is scheduled to be aired in 2019.