When small children imagine that one day they they're going to be an inventor, they have something fairly life-changing in mind.
They want to change the world with their equivalent of the printing press, the light bulb or the internet. Of course in reality, they can't all be Johannes Gutenberg, Thomas Edison or Tim Berners- Lee. Fortunately, they don't have to be.
We've tracked down some inventions which did very little to change the world - and in many cases just filled it with a bit more junk - and yet they earned their inventors millions - and in one case billions.
1. Koosh Balls
These multicoloured balls of fluffy rubber were invented by Scott Stillinger in 1988, to help his kids learn to catch. He went on to sell more than 50 million of them, before selling the company in 1994 for an undisclosed sum which is thought to run into millions. Koosh balls, meanwhile, are still populating the pocket-money sections of toy shops all over the world almost 30 years later.
2. Pet Rocks
Gary Dahl, an advertising executive from California, came up with the ingenious plan of buying pebbles from a construction supplier, decorating them to look like animals, and selling them to children. He used his advertising genius to market them as pets that never needed to be cleaned up after, and he wrote a jokey manual which came with the rocks. The craze hit in 1975 and swept the world. He was said to have made more than £56 million dollars.
Alex Tew came up with a plan in 2005 to fund his business degree at Nottingham University. He bought a web domain and laid out an area of 1 million pixels. Then he offered to sell them for $1 per pixel as advertisements - in $100 blocks. Within five months he had sold the lot and made over $1 million.
4. The Beanie baby
In 1993 Ty Warner, a former soft toy salesman, hit on the idea of under-stuffing mini teddy bears with plastic beads, and selling them in hundreds of different forms (complete with a name and a back-story). They were an instant hit, and Warner is now thought to be worth more than $2.7 billion. Forbes has named him as the 674th richest billionaire in the world.
5. The Slinky
Richard James was working with a tension spring in the mid-1940s when he accidentally dropped it. Watching it slink across the floor, he came up with an ingenious stocking-filler of an idea. Some 300 million of them have been sold since. Much of the toy's success was down to his wife Betty who came up with the name and an advertising jingle - and took over the company 15 years after the invention when James went to live with a religious cult in Bolivia.
6. The Trunki
Rob Law from Bristol came up with the idea for a ride-on, pull-along children's suitcase in 1997, but when he took it to the Dragon's Den in 2006 they turned him down. Since then, the company has taken on 50 people and has a turnover of more than £7 million. It's known as the Den's most successful reject.
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