An early television appearance was as David Balfour in the BBC's 1963 adaptation of Robert Louis Stevenson's Kidnapped, set in Scotland in 1751.
Balfour is captured while on board a ship, and here he meets Jacobite rebel Alan Breck Stewart with whom he forges an alliance, escaping to the Scottish Highlands while trying to avoid the redcoats.
The death of any policeman in real life or fiction was still uncommon in the 1970s and this moment became one of TV's biggest dramatic shocks of the decade.[5][better source needed].
His character Angus Hart, was the original lead of the Channel 5 soap opera Family Affairs, appearing in over 400 episodes.
Cullen's stage work was extensive and saw him perform all over the country, with eight West-End productions to his name and two years with the Royal Shakespeare Company.