Trevor Howard's spy chief character Mostyn evoked his equivalent character 'M' in the James Bond movie franchise due to Mostyn having the same first 'M' letter in his name.

Rod Taylor received top / first billing, Trevor Howard received second billing, Jill St. John received third billing.

According to the 2003 book 'Conversations with Jack Cardiff' by Justin Bowyer and Jack Cardiff, a legal dispute delayed the film's originally intended November 1965 release for about a year, and was not released until late 1966.

Apparently, star Rod Taylor insisted he play his character Boysie Oakes with an American accent as this was where he was at (an American box-office star) at that time in his film career.

Based on the first of the 'Boysie Oakes' novels by John Gardner, published in 1964. There were seven more: Understrike (1965), Amber Nine (1966), Madrigal (1968) Founder Member (1969), The Airline Pirates (1970), Traitor's Exit (1970) and Killer for a Song (1975). After that Gardner took over writing the James Bond series from the late Ian Fleming.

Boysie Oakes' full name was as Brian "Boysie" Oakes.

Composer Lalo Schifrin intentionally composed the score so it would not emulate John Barry's style from the James Bond franchise.

Director Jack Cardiff has said that censors mandated deletion of Rod Taylor's line that said "... it smells like a Turkish wrestler's jockstrap".

First ever filmed adaptation of a John Gardner novel. The second and final one to date would be The Stone Killer starring Charles Bronson.

MGM originally planned a series of Boysie Oakes spy pictures but this fell through.

Producer Jon Penington hired screenwriter Peter Yeldham after both had collaborated on The Comedy Man.

The secret code letter assigned to agent Boysie Oakes is 'L' as in Liquidator.

The title song was sung by Shirley Bassey who had recently sung the title song for the James Bond film Goldfinger.

This '60s spy movie features a black-and-white opening sequence, something the James Bond film franchise would not do until Casino Royale.

This movie co-stars 'Jill St John' as spy chief Mostyn's secretary Iris MacIntosh. St John would go on to play a Bond Girl called Tiffany Case in Diamonds Are Forever.

This movie has never officially been released on home video or DVD but has played on television and the Turner Classic Movie cable channels.

This movie was made and released approximately one year after John Gardner's novel 'The Liquidator' was first published in 1964.

This picture was one of the first of the major studio's big budget spy spoofs of the James Bond series and pre-dates the Matt Helm and Derek Flint spy spoof franchises.

This was the first big spy movie of the 1960s to cast an Australian as its lead secret agent. The movie actually predates the James Bond movie On Her Majesty's Secret Service starring Australian George Lazenby by about four years.