The XYY Man began life as a series of novels by Kenneth Royce featuring the character of William (or Willie) 'Spider' Scott, a one-time cat-burglar who leaves prison aiming to go straight but finds his talents still to be very much in demand by both the criminal underworld and the British secret service. Scott has an extra "y" chromosome that supposedly gives him a criminal predisposition - although he tries to go straight, he is genetically incapable of doing so.
Royce's original books were : The XYY Man (1970); Concrete Boot (1971); The Miniatures Frame (1972); Spider Underground (The Masterpiece Affair) (1973) and Trap Spider (1974), though he returned to the character in the 80s with The Crypto Man (1984) and The Mosley Receipt (1985).
Regular characters included Scott's long-suffering girlfriend Maggie Parsons; British secret service head Fairfax; Detective Sergeant George Bulman, the tenacious policeman who wants nothing more than to see Scott back behind bars; journalist Ray Lynch; gay photographer Bluie Palmer and KGB chief Kransouski.
When the series came to an end, the character of Bulman and Willis were considered popular enough to merit their own spin-off series,Strangers and later (without Willis, except for a cameo in an early episode) Bulman. Kenneth Royce also returned to his Bulman character, writing No Way Back (Hashimi's Revenge) in 1986, and later The Judas Trail (1996) and Shadows (1996).
Although the series depicts someone with XYY Syndrome as having criminal tendencies, actually there is no connection. This was reported by an early academic paper as a result of the conditional probability fallacy, and may have become conventional wisdom in the 1970s, but subsequent research has not found any evidence for it. The subject was also touched on in an episode of the BBC Science Fiction series Doomwatch, 'By the Pricking of My Thumbs...' (1971), written by Robin Chapman.