Now that Brother Angus has told us the legend of C, it's time to gather around THIS GUY HERE and listen to the Legend of Linux.
About 15 years after the Univac guys built Unix on C because it was a funny, funny joke, computers had gotten smaller and easier to buy and not nearly so likely to have chainsaw arms. Not that they were friendly yet or anything, but at least they would talk to you without you sacrificing a goat first and lighting some black candles. And this one guy from Finland named Linus Torvalds, who was at the time (1) a student with practically no sense of humour and (2) deeply unimpressed with the operating system his computer came with, decided to write his own operating system. He wanted it to be kinda like Unix only instead of being for very very expensive computers that you had to hire guys with beards to run for you, it would be for small, pretty cheap computers that you had to be a guy with a beard to want to run yourself.
He posted about it on what passed for an internet back then, and decided that the best way to get people to use his new friend (LOOK MA I BUILT MYSELF A FRIEND that's nice dear, now eat your porridge) would be to give it away. And not just give it away, but give it away so hard that the people he gave it to had to give it away as well.
Giving something away that hard is called 'GPLing it'. You can call it copyleft too, if you want, but don't because you'll embarrass us.
So it turns out that giving away something as useful as an operating system is a good way to make friends with people who think it's impressive to give away an operating system, so now Linus has a lot of friends and people who want to be his friend because they're impressed with him. And he can yell at them if he wants, and all they can really do is yell at other people because if they make Linus angry he'll tell them they're bad and they'll be banished to neverland or something, I don't know I never figured that part out.
And that's why Linux is Linn-ucks and not Line-X, because Linus says his name Linn-us. And that's why it's still no good for people who don't have beards, because it's written mostly by a guy who only wants to be friends with people who are like him, who might have made up their own operating system if he hadn't beaten them to it.
Now someone tell the story of Apple!