Argus Filch was a Squib and the caretaker of Hogwarts School of Witchcraft and Wizardry in the Harry Potter franchise. Filch usually wandered around the school corridors with his cat Mrs Norris, trying to catch students breaking the school rules. He was portrayed by David Bradley.
Filch is first seen near the doors of the Great Hall with his cat Mrs Norris as Dumbledore mentions him during his important announcement to first year students.
When Harry, Ron and Hermione accidentally wander into the third floor corridor, they scamper when Mrs Norris spots them. By the time Filch arrives, they have scampered. Nevertheless, he continues to search for them.
He is next seen later on when he hears a man screaming that came from one of the books Harry opened whilst searching in the Restricted Section for Nicholas Flammel. Filch and Mrs Norris didn't find Harry because he was hidden from sight with the Invisibility Cloak, but they did find his broken lantern and alerts Snape and Quirrell in a corridor.
Filch is then seen escorting Harry, Ron, Hermione and Draco Malfoy to serve their detention to help Hagrid search for a wounded unicorn in the Forbidden Forest. Hagrid is still saddened that Norbert is sent to Romania where Filch doesn't show any sympathy for him, and unnerves Draco about the task to go into the Forbidden Forest.
Filch and Mrs Norris are first seen outside the doors of the Great Hall where they spot Harry and Ron coming up the staircase, after their crash into the Whomping Willow. Filch has Harry and Ron taken to Snape's office, who reprimands them for exposing a flying car to the sight of seven muggles and damaging the Whomping Willow when the car crashed. Fortunately, Dumbledore and McGongall intervene and gave the boys detention.
When Mrs Norris was petrified by Salazar Slytherin's Basilisk, Filch arrives in the corridor and is horrified when he saw his cat petrified. His horror turned to fury when he accuses Harry of murdering her and threatens to kill him, but Dumbledore stops Filch and informs him that Mrs Norris was petrified.
After finding Harry with a petrified student, Filch instantly jumps to conclusions that Harry is responsible for the attacks and informs McGongall who then escorts Harry to Dumbledore's office.
He is last seen in the Great Hall with his cat who was healed by the end of the year, feeling glad that his cat has been revived.
Filch is seen escorting the students to Hogsmeade while McGongall informs Harry that he has to sty behind due to his permission form not signed by the Dursleys. Later on, he is seen rushing with Dumbledore to the scene where the Fat Lady's portrait has been ruined and they find out from the terrified Fat Lady that Sirius Black has entered the castle. Filch then secures the castle and makes his rounds around the sleeping Gryffindors who have to sleep in the Great Hall that same night.
During Dumbledore's speech about the Triwizard Tournament, Filch came bursting in the Great Hall and whispers something into Dumbledore's ear.
Filch is seen participating on helping with the Triwizard Tournament. He doesn't seem to get the gang of firing the cannon, and subsequently annoys Dumbledore a bit. At the Yule Ball, he is seen dancing with his cat Mrs Norris
He is next seen attending the memorial service of Cedric Diggory in the Great Hall.
When Dolores Umbridge became High Inquisitor at Hogwarts, Filch gladly supported her. He then hangs up numerous Educational Decrees that have been passed by the Ministry of Magic. Meanwhile, Umbridge organizes Inquisitorial Squad that consists Filch, Draco Malfoy, and some of the Slytherins to catch out Dumbledore's Army in the act. During much of the Dumbledore's Army's private lessons, they try to catch them, only to fall into trouble in different ways.
He is seen carrying out Professor Trelawnley's luggage out of the castle, because Umbridge has her removed from her position. However, Dumbledore keeps Trelawnley in the castle, since the power of having teachers removed from the premises lies with the headmaster.
Fortunately for Filch, they eventually alert Umbridge along with the Ministry of Magic, and they catch Dumbledore's Army in the Room of Requirement. After Dumbledore escaped arrest, Filch hangs up the last Education Decree and has all of the portraits taken down under Umbridge's orders.
However, Fred and George set off Wildfire Whiz-bangs in the Great Hall and spreads throughout the school, horrifying Filch and Umbridge so much, that they end up covered in blackened soot, and with most of the Education Decrees falling off the wall.
He is next seen in a Daily Prophet photograph where he has to carry out Umbridge's luggage, due to Umbridge being suspended from Hogwarts.
Filch is seen dragging Draco Malfoy into Slughorn's Christmas Party, claiming that he has found him lurking around in an upstairs corridor where Snape gladly escorts Draco away.
Filch came rushing into the Great Hall, alerting to McGongall that students are out of bed, who she severely tells him that the students were supposed to be out of bed. Afterwards, she orders him to escort all of the Slytherins to the dungeons.
Filch helped students leave the school during the Battle of Hogwarts and participated in the battle itself where he suffers an injury. During the one hour armistice, his wound is treated by Slughorn. When everyone sees Harry Potter's "dead" body, Filch has a gloomy expression of his face whilst mourning for Harry, despite his initial hatred towards Harry. However, the battle recommences as Harry awakens from his fake death and after Voldemort dies, Filch is last seen sweeping up the rubble.
He kept his job of caretaker after the Second Wizarding War. Filch is the only one of the Hogwarts staff to stay at Hogwarts Castle during the summer holidays.