If you are even slightly involved with open source then you have heard about Richard M. Stallman, the founder of the Free Software Foundation and the creator of the GPL. Some people idolize him, others think he is too evangelistic. I personally am envious of his hair. It is not fair that someone over two decades older than me should have so much hair when mine is prematurely falling out.
According to the legend, and I have heard this story from countless sources, Richard saw the need for the FSF when in the early eighties the MIT labs that he was working in received a new laser printer. This printer, as with other printers in the lab, was a shared printer. This means that you would send off your job to be printed and then collect it later. The programmers had the source code to the other printers drivers so had modified this code to send a message to the computer that send the print job once the job was done. This new printer did not have the source code included with it so Richard was not able to add this feature which pissed him off. To throw fuel on the fire, some of his associates were working on third party projects and could not share their code with him due to non-disclosure agreements. Richard decided that he didn't want to live in a world where software was controlled by corporations instead of the programmers who wrote the code so started the free software foundation as a way of making sure that there would always be an alternative to closed source software.
As explained in earlier entries, this lead to a problem. Wanting to give away source code is fine, but in order to make sure that the source code remained free you couldn't just give away the source code. What was needed was some way of making sure that the source code always remained free. And the way Richard did this is with something called the GPL.