For longevity alone, David Suchet's Poirot is right up there. The first episode was broadcast in 1989, and 12 seasons later – after a long hiatus and dark rumours of cancellation – ITV finally announced that the remaining novels will be filmed. Thank goodness. Poirot needs things to be neat and tidy: the asymmetry of stopping filming before the books had been finished would have driven him to an early grave.

Agatha Christie grew to dislike Poirot, so she packed him in with supporting characters: Captain Hastings, the car enthusiast and expositional idiot; Inspector Japp, the hapless Scotland Yard representative; and Miss Lemon, the filing queen.

Suchet had big spats to fill when he took on the role of Poirot. Peter Ustinov had already made a good stab at the Belgian detective in films such as Death on the Nile (always useful for playing Six Degrees of Kevin Bacon, because it stars Bette Davis, David Niven and Manimal). And who could forget Albert Finney in Murder on the Orient Express, channeling his inner Englishman abroad and spending the whole film shouting? But if we're looking at cultural penetration, Suchet has Poirot in the bag: he even voices Poirot in a video game of Murder on the Orient Express. (Which is lucky, as the rest of the voice work seems to have been done by whoever was passing and could almost read.)

The earlier Suchet Poirots are based on Christie's short stories, for the most part, and are played with a comic touch and a beautiful art deco look, which belies the fact that Poirot's home (Whitehaven Mansions) is actually in East London, not somewhere the great man usually ventured. Now the novels are getting darker, and so are the adaptations.

Christie's detractors tend to dismiss her as cosy, but how wrong they are. No one is trustworthy in the Christie universe. She is completely happy to have policemen, mothers, and even children as murderers. She is equally happy letting a child drown (Halloween Party). Poirot is a man with a complex moral compass – in the end, he decides not to snitch on the Orient Express killers, because he decides the murder is justified. Christie had written one of fiction's more sympathetic lynch mobs.

Suchet is clearly heading towards Curtain: Poirot's Last Case, which is due to be filmed this year, and which will be the first ever adaptation of this book. I can scarcely wait. It will also reunite Poirot and Hastings for the first time in a decade, so let's hope ITV has got its chequebook out for Hugh Fraser. No other Hastings will be permitted in my house.

Iconic? Well, duh. He has the little grey cells, the moustache, the shiny shoes, the love of symmetry. Also, in Mark Gatiss's adaptation of Halloween Party: "Comment? Dunked?" (NB: you need to say this in a French accent for it to make sense.) Poirot is the original obsessive compulsive detective, and the most famous Belgian in the world.

Duffers? That ending to Murder on the Orient Express, where Poirot has a crisis of his Catholic faith. Stop over-writing Agatha Christie, ITV: she was better at this than you.