Sherlock Holmes movie. Photo / Supplied Expand

Sherlock Holmes movie. Photo / Supplied

Along with Santa Claus and Mickey Mouse, he is one of the three best-known personalities on the planet.

Orson Welles called him "the world's most famous man who never was", though to millions across the globe he was as real as their family doctor.

To a surprising number, he still is. More than 120 years after his first appearance in print, you can recognise him instantly in silhouette: an angular composition of deer-stalker hat, sharp nose and curly pipe.

A dizzy-making who's who of film stars has affected that look, with varying degrees of success: alongside the classic incarnations of the great detective by Basil Rathbone, Peter Cushing and Jeremy Brett, audiences have had to suffer the impersonations of Michael Caine, Peter Cook, Larry Hagman, John Cleese, Tom Baker, even Roger Moore.

Everyone, it seems, has had a turn at being Sherlock Holmes. He has appeared on screen more times than any other fictional character, from the silent-movie period to the present day. And boy, is he present in the present.

Guy Ritchie's long-awaited film, Sherlock Holmes, scheduled for release in New Zealand on Boxing Day, looks set to be a runaway hit. The trailer, showing Robert Downey Jnr (as Holmes), Jude Law (Dr Watson) and Rachel McAdams (as Irene Adler, Holmes' arch-rival from the story A Scandal in Bohemia) disporting themselves in boxing rings and boudoirs, dodging explosions and displaying surprising amounts of naked flesh, amazed audiences at showings earlier in the year, and has been watched by millions on YouTube.

Last month, a rumour circulated that, even before Ritchie's film comes out a sequel is planned, with Brad Pitt as Professor Moriarty. The shamelessly trendy casting takes us some way from the original stories. Downey is too debauched to play Holmes who - despite his cocaine habit - was always ascetic and asexual; Law is too young, callow and knowing to be the decent, slow-on-the-uptake middle-aged doctor; and McAdams, though she looks perfectly acceptable in a whalebone corset, is too saucy to play the steely adventuress, Adler.

Pitt, meanwhile, is simply nobody's idea of a Napoleon of crime. But worse is to come. Columbia Pictures has announced that it is preparing a comedy spoof, produced by Judd Apatow, the golden boy of Hollywood comedy, and starring Sasha Baron Cohen as Holmes and Will Ferrell as Watson. You can hear a collective groan from the world-wide army of Sherlockians at this disrespectful travesty - but of course they themselves have been playing fast and loose with the literal truth for years.

Holmes fans are world-class pedants when it comes to arguing whether or not their hero put an illegal bet on a horse in the story Silver Blaze, but they're far from academic purists.