Keanu Reeves. Slim, dark, handsome, beady-eyed but open-hearted, solid, meticulous and perfectly tailored yet emotionally fragile and fiery of temper, sexually powerful but physically restrained and ascetic, economic of utterance but poetic of soul, firm-jawed, well-muscled, gravel-voiced, snake-hipped, blessed with a deep, dark intellect that does not cheapen itself with reckless verbosity and often sporting a short beard which doesn't quite join up properly. It is small wonder, when you look at the facts, that I have long been considered, by myself at least, the Keanu Reeves of journalism.

I remember awakening to the Keanu in me during the interview for my first job, an 11-grand-a-year filing and tea-making gig at The Daily Telegraph. We were sitting there at Canary Wharf in the office of the Editor, Max Hastings, when the last man out of Hanoi (or the first man into Ikea, or whatever he was) asked us all who we hoped to emulate. And while these inky-fingered hack-school doinks were saying “Hugh Cudlipp” and “Woodward and Bernstein” and “Martha Gellhorn”, I, for no reason I can remember, said: “Keanu.”

And Max said: “Who?”

And I said: “Keanu Reeves.”

And he said: “Ohhh, yes. Of course.”

And Max must have been a fan, too, because I got the job. Either that, or he had never heard of Keanu Reeves, assumed I was naming some hip young underground journalist, and didn't want to appear out of date.

I wasn’t kidding, either. Who didn’t want to be Keanu? It was 1994. With the comedic triumph of Bill and Ted’s Excellent Adventure and the arthouse credibility of My Own Private Idaho both tucked bodaciously under his belt, Keanu was now tousle-headed cop Jack Traven, in blue jeans, sneakers and a red checked shirt, the pert-bottomed all-American innocent who kept the bus above 50mph for a whole movie while fooling Dennis Hopper with a looped video circuit and snogging Sandra Bullock. This was an action hero for the end of a millennium — a razor-jawed brunette from the socio-ethnic borderline who could convey the full range of human emotions just by staring determinedly into the middle distance, which was just as well, because it was all he ever did.

Alas, Keanu then made the terrible mistake of turning down Speed 2, allowing Bullock to steal the show in the equally gripping boat-that-mustn’t-slow-down sequel, and took the role in Much Ado About Nothing which exposed him as nothing more than a talking turnip on legs. By the time of The Matrix he had so thoroughly lost his way that I remember thinking: “If this humourless thug who wears sunglasses indoors and spends his whole time standing on the ceiling is the future of the human race then, frankly, I’m with the robots.” I began to fear that Keanu was one of those actors who have only one decent film in them, like Pelé in Escape to Victory or the whale in Free Willy.

So imagine my delight when I heard he was to take the title role in Constantine. After Colin Farrell as Alexander the Great and Brad Pitt as Achilles, what could be more natural than Keanu as the man who converted Rome? Only Keanu could give credence to the story of the Emperor who saw a vision of the Cross before the Battle at the Milvian Bridge, built a new capital on the Bosphorus and laid the foundations of Christendom. In hoc signo vinces, duuuude.

When I got to the cinema, though, the posters were not promising. It was Keanu, back in his Matrix-period black coat, toting a silver machinegun in the shape of a cross. Under him, the legend: “The wager between Heaven and Hell is on Earth.” Um, like, I totally know that, dude. Are we talking Job, here? Or the temptation of Christ, maybe? Or the sort of sexy apocrypha that Milton worked up into Paradise Lost? The Bible is full of bets. They’re always the Devil’s idea, admittedly, but God just can’t seem to say no if the odds look half tasty. He’s a regular Sky Masterson, is the Lord.

But then the film starts and up come the words: “He who possesses the spear of Destiny holds the fate of the world in his hands — The Spear of Destiny has been missing since the end of World War II . . .” and some present-day Mexican finds it in a hole in the ground in the first frame, wrapped in a swastika, and you realise you are about to watch another rip-off of The Omen crossed with Raiders of the Lost Ark, featuring cohorts of screaming zombies and a load of crypto-biblical bollocks to make it double extra spooky with knobs on.

Keanu plays a Zippo-flicking undead priest-detective-assassin-cum-Marlboro-Man called John Constantine (whenever an action hero has a bit of a whoopsie surname the rule is that his first name has to be John, pronounced “Jaaaarn”), and for the next two hours he is blown against walls by invisible forces he only dimly grasps. As ever in Hollywood movies, leather-bound books are used to show that it’s all very old and mysterious. Nothing freaks out the Yanks more than a book. The genre here is legal-thriller meets classy historical adventure, as succinctly indicated when, mystified by the arrival of the wrong kind of zombie (a “soldier-demon”, I believe it is) Keanu yells to Rachel Weisz, in that gurgling wheeze of his: “Check the scrolls, see if there’s any precedents!”

The exegetical highlight, though, comes when the Angel Gabriel (Tilda Swinton at her most lively since she lay in a glass box at the Serpentine Gallery for a week) tells Keanu: “You’re going to die because you smoked 30 a day since you were 15. You're going to go to hell because of the life you took. You're f***ed.”

But he isn’t. Because at the end Satan reaches into his chest cavity and pulls out his black, wizened, steaming lungs in order to punish him by making him live, and thus possibly fluff his final chance of redemption.

Alas, Keanu did that a long time ago, and if Satan cared anything about humanity (which, of course, he doesn’t) he would have left the cancerous lungs in.

Constantine is on general release on Friday.