A rather cool "creature" in the
Warhammer 40K universe of
Games Workshop, first seen in
Inquisitor.
Basically, becoming one of these things is a big punishment, generally administered for being a heretic and opposing the Ministorum, the imperial church. The subject is implanted with a huge range of technology, the most important parts being implanted weapons, drug dispensers, and a pacifier helm. The original personality is erased, and a new name made up.
The Arco-flagellant is kept calm most of the time by its helm, its brain filled with calming religious symbols etc. When a command word is uttered the helm switches off, and the drug dispensers are activated. Since the arco-flagellant is a criminal its "owner" will not care about any side effects, and so crippling drugs, such as barrage are used.
The result is a freak with superhuman endurance and power that can be directed at enemies. The sample arco-flagellant in the Inquisitor rulebook is called Damien 1427.