The Piranha Brothers were born in the East End slums of London in 1929, on probation, two weeks apart. They were found too mentally unbalanced even for National Service, and became extortionists, running a protection racket after several false starts. It is said that Dinsdale was a gentleman; he bought his mother flowers and, what's more, he knew how to treat a female impersonator. He also enjoyed nailing people's heads to the floor and to coffee tables, and screwing people's pelvises to cake stands. The local chief constable was in his employ, and would help him threaten others with a thermonuclear device. Known associates of the Piranhas included American musical stars, aristocrats, a man named Kierkegaard who bit the heads off whippets, and other gang leaders.
Dinsdale was deeply afraid of Spiny Norman, an (apparently) imaginary hedgehog who, he believed, lived in a hangar at Luton Airport and who "was wont to be about twelve feet from snout to tail, but when Dinsdale was depressed Norman could be anything up to eight hundred yards long." Spiny Norman (created by animator Terry Gilliam) appeared in this sketch growling "Dinsdale" while towering over London landmarks such as Buckingham Palace and Trafalgar Square; the giant hedgehog made brief reappearances in two later episodes.
Doug was the more feared of the two brothers. Luigi Vercotti, a pimp, claims to have seen grown men pull their own heads off rather than speak to Doug – indeed, even Dinsdale feared Doug. This was largely due to his merciless use of sarcasm, dramatic irony, metaphor, pathos, puns, parody, litotes and satire. Many of those menaced by the Piranha Brothers denied any ill will toward them, terrified into compliance with a code of silence.
The Piranhas operated their extortion racket for years, brazenly and without fear of reprisal. However, Dinsdale's fear of Spiny Norman proved to be their undoing, as he decided to solve the problem once and for all by detonating his nuclear device at Luton Airport in February 1966. After this, the Police sat up and took notice of them.
The brothers were finally captured by Superintendent Harry 'Snapper' Organs (played by Terry Jones) of Q Division, who pursued them in a series of disguises including Blind Pew from Treasure Island, the Earl of Gloucester from King Lear, Sancho Panza from Don Quixote, and Ratty from Toad of Toad Hall. However, the Piranha Brothers later escaped, and presumably returned to their life of absurd crime.