Silicon Valley has long bee the home of blue-sky-thinking billionnaires, but perhaps the most out-there is Elon Musk.

When the Pretoria-born 45-year-old space-tech entrepreneur announced his intention to put a million people on Mars by 2025, it was but the latest bold claim in a career built on audacious mission statements and ear-catching off-the-cuff remarks.

As well a million inhabitants, Musk says his Martian colony will have "iron foundries and pizza joints".

It's that kind of chutzpah that has got him where he is today - sitting on an estimated $17.4 billion fortune.

In 1999, Musk founded the company that would become PayPal, netted close to $180 million from its sale to eBay - and went on to found two billion-dollar enterprises: Tesla Motors, the first car manufacturer to launch a fully electric SUV to the general buyer, and SpaceX, his commercial rocket company.

But what else does the man who thinks people will living on Mars within in a decade think about? Here's a taster of Elon Musk's greatest quips.

Musk on… life on Mars