Argus Filch was a Squib and the caretaker of Hogwarts School of Witchcraft and Wizardry since around 1973. Filch usually wandered around the school corridors with his cat Mrs Norris, trying to catch students breaking the school rules and complaining about Peeves the Poltergeist.
In 1992, after Mrs Norris was petrified by Salazar Slytherin's Basilisk, Filch was furious; however, his cat was healed by the end of the year. In 1995, when Dolores Umbridge became High Inquisitor at Hogwarts, Filch gladly supported her. The next year, he was responsible for recognising Dark objects that were brought into Hogwarts.
Filch helped students leave the school during the Battle of Hogwarts in 1998 and participated in the battle itself. 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.