The author of this article is also the author of this book on Fermat's Last Theorem: http://www.amazon.co.uk/Fermats-Last-Theorem-Simon-Singh/dp/...

Given the eventual proof of Fermat's last theorem there's a solid argument that Fermat hadn't successfully proved it (and certainly couldn't have in the way it was eventually done), but it's also far from clear whether he actually believed he had.

The history of the Theorem and the attempts to crack it, and how Wiles finally got there is fantastic, and if you've not come across it in detail then I'd definitely recommend finding out more about it.

If anyone is looking for a good book about the history of Fermat's Last Theorem I can thoroughly recommend Simon Singh's book about it [1], which is both accessible for those without a strong maths background (like myself) and paints a wonderful history of mathematics as well. In places it's more entertaining than fiction.

[1] http://www.amazon.co.uk/Fermats-Last-Theorem-confounded-grea...