The sleep of reason breeds monsters, and one of the most alarming creatures dreamed up by our irrational culture is the stogy-puffing bogey Arnold Schwarzenegger. He is the spirit of the age made flesh, and his careers as athlete, actor and politician have dramatised its most disturbing paradoxes  the showdown between technology and human nature, the reduction of art to self-marketing, the transformation of government into a branch of showbiz. His surname, translated, means "black corner": he is the dead end at which the evolution of our species and the development of our society have abruptly arrived.

Arnie's very existence is a vindication of the Third Reich's values. Born in 1947 in defeated Austria, he is, as he once admitted, an unrepentant admirer of Hitler's oratory, and while still a teenager  after experimentally crashing some tanks during his military service, fine preparation for his later Hollywood stunts  he devised his own way of prosecuting the Führer's campaign of conquest. His body would be his weapon of war: he lifted weights until he had "deltoids like cannonballs" and "a chest like a fortress". "I aimed to be a leader some day," he balefully growls, and he became one when he won the Mr Universe championship. "Just get out of the fucking way," he warned the puny pretenders who dared to challenge him.

He is frank about his fantasy in this unashamed book, which is an epic of the revved-up ego: "I pictured myself high up on the pedestal, trophy in hand. Everyone else would be standing below. And I would look down." Could the eloquent Adolf have put it better? Arnie's agenda extended that of the Panzer divisions that trampled Europe. "I planned," he announced after recruiting a few foreigners to the Munich gym where he trained, "to go global with everything that I wanted to do."

Here was the unimpeded triumph of the will. In fact the idea of will  the ruthless energy that makes him compare himself to a locomotive  is so important to Arnie that when filming The Terminator he initially refused to contract that sacred word. Tone-deaf and still inept in English, he refused to utter the Terminator's threat "I'll be back" and instead insisted on saying "I will be back". It sounded more rugged, he told James Cameron; "I'll" surely had to be effeminate. Cameron managed to persuade him that an apostrophe was no threat to his virility.

Little Austria couldn't contain Arnie for long. "America," he decided while still at school, "was the most powerful country, so I would go there." He imagined it as a facsimile of his bulging, steroid-boosted physique: "For me, America meant one thing  size." In skittish moods, he likes to think that his mother might have been impregnated by a GI from the occupying army after the war: then he'd be a native-born American, and could run for the presidency. We can only hope that Frau Schwarzenegger did not allow herself to be Americanised in the back of a jeep.

As soon as Arnie hit the ground, he set about purchasing swathes of his new homeland. His goals included finding "an apartment building to buy and move into". Note the order of business: you can hardly imagine him modestly renting a room. Next he bought a portion of desert outside LA, the site for a projected supersonic airport that was  like Arnie himself  "monstrous, very futuristic, exactly what I imagined America was about". Then came cinematic stardom. Arnie advanced from Conan the Barbarian to The Terminator, in which he was typecast as a machine: like the United States itself, he went straight from barbarism to decadence, overleaping the intermediate stage known as civilisation.

Power in our culture depends on imagery and publicity, so political office almost automatically followed. The first President Bush made Arnie, as he puts it with his usual absolutism, a "fitness czar". This latter-day Romanov would never be unseated by a red revolution: his mantra, on and off screen, is "Fucking communists, I despise them". When California elected him its Governator, he understood this to be just another acting role. The blissed-out citizens of the Golden State could have done worse, of course: attempts were made to convince Mel Gibson to run against him in the 2006 Republican primary.

Arnie's political philosophy was crassly testicular. "Change," he declared, "takes big balls," and he grafted those organs on to women he approved of: among the "ballsy people" on his gubernatorial staff was "a small, tough, blonde, cigar-smoking lesbian". A little more incongruously, he remarks about his wife: "One side of Maria was ballsy." Apparently she had an eggy side as well, since their marriage produced four children, supplemented by an extra son who was mothered by a housekeeper. Clive James once famously said that the bodybuilding Arnie looked like a condom stuffed with walnuts; when he and his employee Mildred coincided in a guesthouse attached to the marital mansion, the condom apparently split and what leaked out was a peanut-sized replica of the Impregnator. Arnie has put the embarrassment behind him. "I have to keep moving forward," he says: he's a locomotive, remember.

He takes pride in his automated efficiency, boasting that once at Cannes he gave 40 TV interviews and 54 print interviews  all of them, I bet, exactly the same  in a single day. Or is he, despite his steely post-human implacability, actually one of the "subhuman thugs" who maraud through Conan? While making Terminator 2, he often questioned Cameron about the existential status of the character he was playing: "Is he too human now, or not human enough?" It's what I asked myself after finishing this book, which is self-obsessed without being self-aware. I decided that Arnie's megalomania must be superhuman, since his memoir contains no trace of the apologetic irony that redeems some of his films. He is, notwithstanding the efforts of a "coauthor" implausibly named Peter Petre, a machine without a ghost inside him.