9. Clyde Alexander Shelton (Law Abiding Citizen)
Overture FilmsWhat makes Clyde stand out from the majority of the entries in this list in motivation: it's not money or fame or respect he's after, it's good ol' fashioned revenge. Clyde's family were brutally slain by a pair of crooks during a home invasion and the criminal justice system allowed one of them to walk despite having hard DNA evidence on both men. Cut to ten years later and both criminals and the members of the justice system involved in the verdict start dropping like flies. Clyde then gives himself up to the police as the perpetrator but even behind bars, people keep getting killed off in inventive and grisly ways. We discover it's all Clyde's doing: he used to come up with crazy and brilliant ways to assassinate people for the CIA and now he's turned his creative talents to sweet, sweet revenge. Poison, car bombs, he even weaponises a goddamn bomb disposal robot to kill a guy, all from the confines of solitary confinement. In the end, his own thirst for vengeance is his undoing. For the bulk of the movie though, he has everyone, including the audience, stumped as to just how he's pulling off these murders from behind bars.