Thunderball was originally planned as the first movie in the James Bond franchise from producers Albert R. 'Cubby' Broccoli and Harry Salzman. However, 'Thunderball' became embroiled in a legal dispute with Kevin McClory and Jack Whittingham - two former collaborators of 007 creator, Ian Fleming. The pair sued the author shortly after the publication of the 'Thunderball' novel in 1961.
McClory and Whittingham claimed Fleming had based the 'Thunderball' book on a screenplay the triumvirate had created together. Fleming apparently did not have the will to fight the legal challenge, and settled the matter out of court. As a consequence, Kevin McClory was awarded the screen rights to Thunderball's plot and characters. Fearing McClory might launch a rival 007 movie at a time when they were building up the franchise, Broccoli and Salzman granted him a sole producer credit and settled for executive producer credits instead.
Famously, in 1983, McClory also released a second on-screen adaptation of 'Thunderball' under the title, 'Never Say Never Again'. The movie starred Sean Connery twelve years after he had left the official James Bond franchise and competed directly against 'Octopussy', starring Roger Moore as 007. Much to the relief and satisfaction of the EON production team, 'Octopussy' outperformed the unofficial movie at the worldwide box-office.