The show starred American Steve Forrest as John Mannering, an antiques dealer and undercover agent working in an informal capacity for the head of the fictional British Diplomatic Intelligence, Templeton-Green (Colin Gordon). Paul Ferris was originally cast as Mannering's assistant David Marlowe. However after pressure from the US network Marlowe was dropped in favour of the more glamorous Cordelia (Sue Lloyd) who had appeared in the first episode.
In Creasey's original novels Mannering was British and, after the few first entries, married. In transforming him into a bachelor and casting a Texan in the role, the producers decided that 'The Baron' would be nicknamed after the cattle ranch once run by his grandfather. In the books he was a reformed jewel-thief (the first few novels described that "career" from Mannering's decision to steal to his going straight) whose criminal ties served him well in investigating jewel, art or antiques-oriented mysteries.
Like other ITC shows, The Baron shared a lot of its production crew with the other productions of the time (Danger Man, The Saint etc.), including guest cast members Peter Wyngarde and Bernard Lee, and directors Roy Ward Baker and Robert Asher. The lion's share of the scripts were by Dennis Spooner and Dalek creator Terry Nation. A few episodes were written by 'Tony O'Grady', none other than The Avengers writer-producer Brian Clemens under a pseudonym.
The character of Mannering was like Simon Templar, a member of the jet set, whose glamorous lifestyle was typified by the (at the time) still-exclusive air travel to exotic locations. However filming never left the UK; indeed was filmed chiefly in and around Elstree Studios in Borehamwood in Hertofrdshire. Locations used included Haberdashers' Aske's School, St. Albans and Ivinghoe Becon. These featured prominently in several other ITC series of the same era. The backlot at Elstree in particular was extensively used, being transformed alternately into Mannering's antiques shop, a Mexican town, a Parisian nightclub, an East European police station and many others besides.
As with other ITC series, the American market was vital, and several episodes were overdubbed (e.g. 'petrol' becoming 'gas', 'whisky' becoming 'scotch') to ensure it was fit for US audiences. Unfortunately despite a promising start it did not do well enough on the US network and was syndicated midway through its run. This effectively ensured no second series would be made even though it was well received in the UK.
The Baron's car was a silver Jensen CV-8 MII with the registration 'BAR 1'. Unlike the Volvo driven by The Saint, the exclusivity of the car meant the series did not generate the same sales boost as The Saint had done for Volvo. Cordelia drove a considerably less upmarket Daf33.
The episode Something For A Rainy Day featured a clip of the now-famous white Jaguar plummeting over a cliff. It was apparently filmed for this episode but was deemed so expensive the clip went on to be used in many episodes and series later, effectively becoming an in-joke. Whenever someone got in a white Jaguar it inevitably ended in doom!
The episode Portrait of Louisa was a reworking by Terry Nation of his earlier script for an episode of The Saint entitled "Lida."