The caretaker of Hogwarts School of Witchcraft and Wizardry in the popular Harry Potter series by J.K. Rowling. He's not very friendly to students and takes every opportunity he can to catch them breaking the rules. His cat, Mrs. Norris, helps him by prowling the corridors in search of any students out after hours or breaking rules. When Filch does manage to catch someone, his/her punishment often involves helping him in his caretaker duties, which include cleaning and polishing.
Although he is a pure-blood, Argus never became a wizard because he was born without magical powers. This is not very common for those born to wizarding parents, and can be rather embarrassing if it is found out, so Filch, as Harry found out, tried to learn magic by correspondence course to avoid the unfortunate circumstance of being what is called a Squib. His lack of wizarding ability may be part of the reason that he is so hostile towards Hogwarts students.