Alan Armstrong (born 17 July 1946), known professionally as Alun Armstrong, is an English actor. Armstrong grew up in County Durham in North East England. He first became interested in acting through Shakespeare productions at his grammar school. Since his career began in the early 1970s, he has played, in his words, "the full spectrum of characters from the grotesque to musicals... I always play very colourful characters, often a bit crazy, despotic, psychotic".

His numerous credits include several different Charles Dickens adaptations and the eccentric ex-detective Brian Lane in New Tricks. Armstrong is also an accomplished stage actor who spent nine years with the Royal Shakespeare Company. He originated the role of Thénardier in the London production of Les Misérables and he won an Olivier Award for playing the title role in Sweeney Todd.