In 1988, Robert W Faid solved one of the oldest and most famous problems in mathematics. Yet almost no one noticed. Cracking the nut that was nearly two millennia old, Faid calculated the identity of the Antichrist.

In the rarified world of mathematicians, certain problems become the focus of intense pursuit. The four-color map problem was finally solved, by Wolfgang Haken and Kenneth Appel, in 1976. Fermat's last theorem tantalised mathematicians until Andrew Wiles solved it in 1993. Haken and Appel became instantly famous among mathematicians. Wiles became a worldwide celebrity.

But little academic or public acclaim came to Faid, perhaps because no one had previously realised that the identity of the Antichrist was a mathematical problem.

In fact it has been on the books since about the year AD90, when the Revelation of St John brought it to public notice. Over the years, many amateur mathematicians joined the professionals in trying their hand at this delightful yet maddening puzzle. Eventually it became a favourite old chestnut, something to be wondered at, but perhaps too difficult ever to yield up a solution.

Then, after most had given up hope, Faid solved it. In retrospect, his accomplishment seems almost absurdly simple: the Antichrist is Mikhail Gorbachev, with odds of 710,609,175,188,282,000 to 1.

There is no mystery to this. Faid is a trained engineer. He is methodical and rigorous. He wrote a book explaining every first and last tittle and jot. Gorbachev! Has the Real Antichrist Come? was published by Victory House. It tells where each number comes from, and how it enters into the calculation. Professional mathematicians find it difficult to argue with the logic.

Outside the maths community, the book received little attention, but five years later, Faid was awarded an Ig Nobel Prize for his achievement.

Recently another good and great mathematical problem was knocked off. Stephen D Unwin wrote a book called The Probability of God. It is much celebrated.

Unwin has a PhD in theoretical physics. Like Faid, he has methodically, rigorously, and with faithful certainty chosen some numbers, then performed addition, subtraction, multiplication and division. The calculated result: that there is almost exactly a 67% probability that God exists. The book reveals all the technicalities, and includes a handy spreadsheet for those anxious to try the calculations for themselves. And like all good statistical reports, it points out the possibility that something is off. There is, Unwin carefully warns us, a 5% chance that his calculation is wrong.

Faid, Unwin, and God knows how many others give mathematicians faith that every problem, no matter how hard, can have some kind of devilishly simple solution.

· Marc Abrahams is editor of the bimonthly magazine Annals of Improbable Research (www.improbable.com), and organiser of the Ig Nobel Prize