Originally meant as the first 'James Bond' film, 'Thunderball' was the center of legal disputes that began in 1961 continued up until 2006. Former 'Ian Fleming' collaborators, 'Kevin McClory' and 'Jack Whittingham', sued him shortly after the 1961 publication of the Thunderball novel, claiming he based it upon the screenplay the trio had earlier written in a failed cinematic version of James Bond. The lawsuit was settled out of court.
McClory retained certain screen rights to the novel's story, plot, and characters. By then, James Bond was a box office success, and series producers 'Albert R (Cubby) Broccoli' and 'Harry Saltzman' feared a rival McClory film beyond their control. They agreed to McClory's producer's credit for the big-screen version of Thunderball, with them as executive producers. The sources for Thunderball are controversial among film aficionados. In 1961 Ian Fleming published his novel based upon a film screenplay. The efforts were unproductive and Fleming expanded the script into a James Bond novel. Consequently, one of his collaborators, Kevin McClory, sued him for plagiarism. They settled out of court in 1963.
Later, in 1964, EON producers Broccoli and Saltzman agreed with McClory to cinematically adapt the novel. It was promoted as "Ian Fleming's Thunderball". To date, Thunderball has twice been adapted cinematically; Firstly in 1965's Thunderball and secondly, in the 1983's, McClory-produced, 'Never Say Never Again', both featuring 'Sean Connery' as James Bond.
Originally, the film was scheduled for release in direct competition with the EON Bond film, 'Octopussy' starring 'Roger Moore' which led to the media dubbing the situation "The Battle of the Bonds". Ultimately, the two films were released at different points in 1983 and both were big box-office successes, though Octopussy was the 'winner', making $187 million compared to the $160 million made by Never Say Never Again.
The title was based on a conversation between Sean Connery and his wife. After Diamonds Are Forever he told her he'd 'never' play James Bond again. Her response was for him to "Never say never". She is credited at the end of the film for her contribution. As a result, it was the first Bond movie to use a non-Fleming originated title.