The most famous example that I know about is Samuel Langhorne Clemens, or Mark Twain as everyone knows him. When he wasn't writing classic novels like The Prince and the Pauper, A Connecticut Yankee in King Arthur's Court and all those Tom Sawyer and Huckleberry Fin books, Twain fancied himself as a bit of an inventor. Believe it or not, Twain patented three different inventions, the most successful of which was a self-pasting scrapbook. Seeing as he was quite good friends with Nikola Tesla, and the two reportedly hung out together in Tesla's lab, this is perhaps not surprising, but definitely unusual for a writer!

Plenty of authors have hobbies as you can't spend all your time writing. Most of these hobbies are quite ordinary, like Victor Hugo, the writer of Les Miserables, who also painted and Ernest Hemingway who wasn't averse to a spot of hunting and fishing. The authors with hobbies that I would consider slightly more unusual would be Sylvia Plath, who wrote The Bell Jar, and then decided to take up beekeeping, as well as H. G. Wells who wasn't ashamed to admit that he was a war gamer. Bear in mind, this is a hobby that is considered extremely geeky even in this day and age, so imagine the reaction that Wells got in his time for mucking about with clockwork trains and toy cannons.

It was probably closer to an obsession than a hobby, but the author of The Hobbit had a thing for ancient languages. It helped him though as he actually invented a few languages for his books, including Elvish, Entish and Dwarvish.

Agatha Christie liked to get her hands dirty with archeology.

Victor Hugo was actually a very good painter.

Leo Tolstoy was a talented chess player.

Ernest Hemmingway enjoyed deep sea fishing.

J. R. R. Tolkien described his passion for inventing languages as a "mad hobby."

Ayn Rand was an avid stamp collector.

Vladimir Nabokov chased butterflies around with a net in his spare time.

Franz Kafka was a collector of some rather dirty books

My favorite example of an author that had a pretty peculiar hobby was Charles Dickens and his Ghost Club. I have a hard time picturing Dickens stomping around like a Victorian era Zak Bagans while looking for ghosts, but the purpose of the club was apparently to investigate all kinds of ghosts and hauntings. Dickens must have been quite important for the club too as it dissolved after his death. The real mystery is how much investigating of spirits the club did versus how much socializing with a few bottles of spirits!