Ayn Rand: Can two new biographies unravel the mystery of the mad, sad heroine of the American right?

Ayn Rand is one of America's great mysteries. She was an amphetamine-addicted author of sub-Dan Brown potboilers, who in her spare time wrote torrents of praise for serial killers and the Bernie Madoff-style embezzlers of her day. She opposed democracy on the grounds that "the masses" - her readers - were "lice" and "parasites" who scarcely deserved to live.

Yet she remains one of the most popular writers in the US, still selling 800,000 books a year. She regularly tops any list of books that Americans say have most influenced them. Since the great crash of 2008, her writing has had another Benzedrine rush, as Rush Limbaugh hails her as a prophetess. With her assertions that government is "evil" and selfishness is "the only virtue", she is the patron saint of doomsters. So how did this little Russian bomb of pure immorality in a black wig become an American icon?

Two new biographies of Rand, Jennifer Burns's Goddess of the Market (Oxford, £16.99) and Anne Heller's Ayn Rand and the World she Made (Nan A Talese), try to puzzle out this question, showing how her arguments found an echo in the darkest corners of American political life. They are thrilling psychological portraits of a horribly damaged woman who deserves the one thing she spent her life raging against: compassion. Alisa Rosenbaum was born in the icy winter of Tsarism, not long after the failed 1905 revolution ripped through her home city of St Petersburg. Her father was a self-made Jewish pharmacist, her mother an aristocratic dilettante who loathed her three daughters. She would tell them she never wanted children.

Alisa became a surly, friendless child. In elementary school, her class was asked to write an essay about why being a child was a joyous thing. She instead wrote "a scathing denunciation of childhood" headed with a quote from Pascal: "I would prefer an intelligent hell to a stupid paradise."

The worst anti-Jewish violence since the Middle Ages was brewing, and the family was terrified of being killed by the mobs. But it was the Bolsheviks who struck at them first. After the 1917 revolutions, her father's pharmacy was seized. For Alisa, who had grown up surrounded by servants and nannies, the Communists seemed at last to be the face of the masses, a terrifying robbing horde. In a country where five million people died of starvation in two years, the Rosenbaums went hungry. Her father tried to set up another business, but after it too was seized, he declared himself to be "on strike".

The Rosenbaums knew their angry, outspoken daughter would not survive under the Bolsheviks for long, so they arranged to smuggle her out to relatives in America. Just before her 21st birthday, she said goodbye to her country and her family. She was determined to live in the America she had seen in the silent movies – of skyscrapers, riches and freedom. She renamed herself Ayn Rand, a name she thought had the hardness and purity of a Hollywood starlet.

She headed for Hollywood, where she set out to write stories that expressed her philosophy: a body of thought she said was the polar opposite of communism. She announced that the world was divided between a small minority of Supermen and "the naked, twisted, mindless figure of the human Incompetent" who, like the Leninists, try to feed off them. It is evil to show kindness to these "lice": the "only virtue" is selfishness.

She meant it. Her diaries from that time, while she worked as a receptionist and an extra, lay out the Nietzschean mentality that underpins her later writings. The newspapers were filled for months with stories about serial killer William Hickman, who kidnapped a 12-year-old girl called Marion Parker, raped her, and dismembered her body, which he sent mockingly to the police in pieces.

Rand wrote great stretches of praise for him, saying he represented "the amazing picture of a man with no regard whatsoever for all that a society holds sacred, and with a consciousness all his own... Other people do not exist for him, and he does not see why they should." She called him "a brilliant, unusual, exceptional boy". Rand had only one regret: "A strong man can eventually trample society under its feet. That boy [Hickman] was not strong enough."

It's not hard to see this as a kind of political post-traumatic stress disorder. Rand believed the Bolshevik lie that they represented the people, so she wanted to strike back at them through theft and murder. In a nasty irony, she was copying their tactics. She started to write her first novel, We the Living, and in the early drafts her central character - a crude proxy for Rand herself - says to a Bolshevik: "I loathe your ideals. I admire your methods. If one believes one's right, one shouldn't wait to convince millions of fools, one might just as well force them."

She poured these beliefs into a series of deeply odd novels. She takes the flabby staples of romantic fiction and peppers them with political ravings and rapes. All have the same core message: anything that pleases the Superman's ego is good; anything that blocks it is bad. In The Fountainhead, published in 1943, a heroic architect called Howard Roark designs a housing project for the poor - not out of compassion but because he wants to build something mighty. When his plans are slightly altered, he blows up the project, saying the purity of his vision has been contaminated by evil bureaucrats.

For her longest novel, Atlas Shrugged, Rand returned to a moment from her childhood. Just as her father once went on strike against Bolshevism, she imagined the super-rich in America going on strike against progressive taxation - and said the US would swiftly regress to an apocalyptic hellhole if the Donald Trumps and Ted Turners ceased their toil. The abandoned masses are described variously as "savages", "refuse" and "inanimate objects". One of the strikers deliberately causes a train crash, and Rand makes it clear she thinks the murder victims deserved it, describing in horror how they all supported the taxes that made the attack necessary. Her heroes are a cocktail of extreme self-love and extreme self-pity. They insist they need no one, yet spend all their time fuming that the masses don't bow down before their manifest superiority.

As her books became mega-sellers, Rand surrounded herself with a tightly policed cult of young people. They were required to memorise her novels and slapped down as "imbecilic" if they asked questions. Rand had become addicted to amphetamines while writing The Fountainhead, and her paranoia and aggression were becoming more extreme. Anybody who disagreed with her was subjected to a show trial in which they would be required to repent or face expulsion. Her secretary, Barbara Weiss, said: "I came to look on her as a killer of people." The cult exposed the hollowness of Rand's claims to venerate free thinking and individualism. Her message was: think freely, as long as it leads you into total agreement with me.

In the end, Rand was destroyed by her own dogmas. She fell in love with a young follower, Nathaniel Branden, and had a decades-long affair with him. He became the cult's No. 2, and she named him as her "intellectual heir" - until he admitted he had fallen in love with a 23-year-old woman. As Burns explains, Rand's philosophy "taught that sex was never physical; it was always inspired by a deeper recognition of shared values, a sense that the other embodied the highest human achievement." To be sexually rejected by Branden meant he was rejecting her ideas, her philosophy, her entire person.

She never really recovered. We all become weak at some point in our lives, so a thinker who despises weakness will end up despising herself. In her seventies Rand found herself dying of lung cancer, after insisting that her followers smoke because it symbolised "man's victory over fire" and the studies showing it caused lung cancer were Communist propaganda. By then she had driven almost everyone away. In 1982, she died alone in her apartment with only a hired nurse at her side. If her philosophy is right - if the only human relationships worth having are based on the exchange of dollars - this was a happy and victorious death. Did even she believe it in the end?

Rand was broken by the Bolsheviks as a girl, and never left their bootprint behind. She believed her philosophy was Bolshevism's opposite, when in reality it was its twin. Both she and the Soviets insisted a small elite in possession of absolute rationality must seize power and impose its vision on a malleable, imbecilic mass. The only difference was that Lenin thought the parasites to be stomped on were the rich, while Rand thought they were the poor.

I feel sympathy for Rand, even as I know she would have spat it back into my face. What I do find incomprehensible is that there are large numbers of people who see her writing not as psychopathy but as philosophy, and urge us to follow her. Why? Unfortunately, neither of these equally thorough, readable books can offer much of an answer to this great question about her. Rand expresses, with a pithy crudeness, an instinct that courses through us all sometimes: I'm the only one who matters! I'm not going to care about any of you! She then absolutises it in a Benzedrine-charged reductio ad absurdum by insisting it is the only feeling worth entertaining, ever.

This urge exists everywhere, but it is supercharged on the American right. We all live every day with the victory of this fifth-rate Nietzsche of the mini-malls. Alan Greenspan was one of her strongest cult followers and even invited her to the Oval Office to witness his swearing-in when he joined the Ford administration. You can see how he carried this philosophy into the 1990s. Why should the Supermen of Wall Street be regulated to protect the lice of Main Street?

The figure Ayn Rand most resembles in American life is L Ron Hubbard, another crazed, pitiable charlatan who used trashy potboilers to whip up a cult. Unfortunately, Rand's cult isn't confined to Tom Cruise and a rash of Hollywood dimwits. No, its ideas and its impulses have, by drilling into the basest human instincts, captured one of America's major political parties.