The duo, who live in New York, have each built personal fortunes estimated at ?50 million from the ultra-violent series, in which players assume the identity of ruthless underworld criminals.
Despite (or perhaps because of) its controversial depiction of sex, violence, rape, car-jacking, drug dealing, torture and murder, GTA ? as it is known to aficionados ? has shifted more than 135 million units since its 1997 debut.
Among the many eureka moments which led to GTA's success was an innovation (introduced for the third instalment of the game, released in 2001) allowing players to increase their character's health by having sex with a prostitute. They could then advance in the game by beating or murdering the prostitute and stealing her money.