FORM follows function. Mercedes-Benz may embrace this slogan in its advertising, but Gunther Holtorf has lived it for 17 years and more than half a million kilometres.

The phrase refers to the construction of the Mercedes-Benz G-Class, an off-road vehicle that looks like it was penned by a five-year-old who has yet to grasp the concept of a curve.

Mr Holtorf bought one such boxy-looking G-Class in 1988 for the equivalent of 30,000 euros (S$62,000 at today's exchange rate). In 1990, he took out the back seat and drove his Mercedes-Benz 300 GD, named Otto, to what would be the first of 130 countries he would end up visiting.

Now 70, the German globetrotter spends about half a year on the road with his wife and Otto. They have travelled through Africa and South America, and up the North American continent to Alaska.

Mr Holtorf was in Singapore last week after driving down from Malaysia, and they hope to finish all their travels by mid-2009, after visiting the Caribbean, China and Japan.

Through all those thousands of kilometres around the world, Otto has transported him, housed him and carried his supplies.

'It is a car built to make use of all the space available,' he explains. 'There are no fancy curves; it's a boxy car with a lot of space. It's a functional car and that's what I like.'

'The German adventurer says it is unlike modern cars, which are built according to a different philosophy.

'The G-Class was built to last under real adverse conditions. The car has never let us down. Certainly, there have been some snags but I've always been able to fix them.'

In addition to a load of 400 kg on Otto's roof, Mr Holtorf also carries a collection of about 450 small and large original spare parts. Also on board are the necessary tools and manuals to service the car, and rescue equipment like a manual winch in case it gets stuck in sand, mud or water.

The rugged 300 GD has an 88 hp diesel engine and although it is old, it is simple in mechanical terms and totally reliable. While most models of its vintage would clock up 200,000 or 300,000 km, Otto has racked up 600,000.

'There have been no modifications - the car is original from A to Z,' he says. 'The only thing we did was to take out the rear bench, so that there are only two seats in the car.'

The extra space allows two people to sleep in the back.

'In Malaysia and Cambodia, we slept in the car because we have mosquito nets. In South America, we slept outdoors in hammocks.'

Mr Holtorf used to work for Lufthansa and Hapag-Lloyd before he began travelling. He drives for about half the year, then leaves the car with a storage company before returning to Europe, then goes back to it to continue his travels.

When he finally winds down in two years' time, he says he will apply for an entry in the Guinness Book of World Records while Otto will find a parking spot in the new Mercedes-Benz museum in Stuttgart as a permanent exhibit.

'It will be a showpiece in the biggest automotive museum on Earth.'

A fitting tribute to a car that has gone around it.