Once upon a time there were three billy goats, who were to go up to the hillside to make themselves fat, and the name of all three was “Gruff.”
On the way up was a bridge over a cascading stream they had to cross; and under the bridge lived a great ugly troll , with eyes as big as saucers, and a nose as long as a poker.
So begins The Three Billy Goats Gruff, a classic Norwegian tale of gluttony and violence , which is, after all, par for the course as far as fairy tales go. And the best fairy tales pull no punches when it comes to being profane, scary, politically incorrect, and generally unwholesome for little girls and boys.
Or so one might think.
The tendency for well-meaning modern writers to “reinterpret” such stories so that they don’t harm the fragile psyche of the child misses the point; that the fragile psyche actually needs to be damaged. Or at least shaken around a little.
In his classic book, The Use of Enchantment: The Meaning and Importance of Fairy Tales, the child psychologist Bruno Bettelheim does an amazing job of explaining why such tales are important to the psychological development of children, and how their often dark and upsetting subject matter is actually a way for kids to learn to deal with the harsh realities of life.
And this desire to “protect our children” is why many of the current version of the Three Billy Goats Gruff end up with the troll who lives under the bridge being pushed into a river – a significant difference from the original fate of the hapless bridge-dweller. Here’s how the third of the goats disposes of the troll;
And then he flew at the troll, and poked his eyes out with his horns, and crushed him to bits, body and bones, and tossed him out into the cascade, and after that he went up to the hillside.
There’s little chance of “swimming to safety” or “just getting a wee bit wet” here. The goat clearly has an agenda, and the almost ritualistic killing would look a little distressing in a kid’s picture book. It’s also unclear what the troll had actually done to deserve such a brutal slaying. Sure, he’d threatened to eat the goats but they were, after all, trespassing on his bridge.
In Scandinavian mythology, a troll is an ugly and malevolent creature, larger than humans but with a taste for their flesh. They live in caves (and apparently also under bridges) and only come out at night, otherwise they turn to stone in sunlight.
The word comes from the Old Norse troll meaning a giant or a demon, but there is also the Old Norse word trolldomr meaning witchcraft. The Swedish trolla means “to charm or bewitch,” so the link between troll and some supernatural element is clear. 
And it’s this sense of the word troll that forms the basis of the modern term, patent troll. In the legal world, a patent troll is a person or company that buys patents for the sole purpose of using them strategically in order to sue others who infringe – or appear to infringe – the patent. The trick for a patent troll is to look for cheap patents (usually from a company going bankrupt) and keep them until there’s an opportunity to use them. If an innocent third-party invents something new that appears to be covered by the patent, the troll will “jump up” and surprise them with a huge claim, usually in the millions.
There is a twist to this use of the word that depends on another meaning of the word troll that comes from the fishing world. The Oxford English Dictionary suggests that this originates from the Old French troller, which means;
To move or walk about or to and fro; to ramble, saunter, stroll, ‘roll’; spec. (slang) of a homosexual: to walk the streets, or ‘cruise’, in search of a sexual encounter.
Now no-one is suggesting that the slang notion applies to patent trolls – although I’m sure folks who have been sued by them may well be inclined to favor it – but the “moving about” and “rambling” lent itself to describing the activity of pulling a single line behind a boat to try to catch fish. This choice of word may also have been influenced by the similar-sounding word trawl, which means to fish using a net with the intent of pulling it through the water to trap sea creatures.
The word trawl derives from the Middle Dutch traghelen, meaning “to drag,” which may, in turn, come from the Latin tragula, a dragnet. Thus, although troll and trawl may both be fishing words and have similar functions, the words come from different roots.
The idea of “trolling for fish” was extended to include “trolling for ideas or information.” And this, in turn, lead to the modern notion of an internet troll, which the OED defines as;
A person who posts deliberately erroneous or antagonistic messages to a newsgroup or similar forum with the intention of eliciting a hostile or corrective response.
The person is either seen as (a) behaving like a troll, waiting to “jump up” and pick a fight, or (b) trolling for responses. However, just to make things even more confusing, if you are surfing the net to accumulate lots of pieces of data, you are “trawling the net,” not “trolling”; the two things are different. Here’s how the OED defines this newer meaning of trawling;
To engage in an exhaustive or extensive (sometimes indiscriminate) search for something.
So let me summarize the various definition we’ve encountered:
1. troll (mythology): a Scandinavian ogre who eats people.
2. troll (law): an attorney who uses patents to sue people.
3. troll (slang): a homosexual who cruises the streets to have sex with people.
4. troll (internet): a person who posts outrageous comments to bait people.
5. troll (fishing): to drag a single line behind a boat to catch fish.
6. trawl (fishing): to drag a net through water to catch anything.
7. trawl (informatics): to hunt for information.
Who would have thought such confusion could come from simply cross a rickety, rackety bridge.
 English translation at http://www.pitt.edu/~dash/type0122e.html#gruff: Peter Christen Asbjørnsen and Jørgen Moe, De tre bukkene Bruse som skulle gå til seters og gjøre seg fete, Norske Folkeeventyr, translated by George Webbe Dasent in Popular Tales from the Norse, 2nd edition (London: George Routledge and Sons, n.d.), no. 37, pp. 275-276. Translation revised by D. L. Ashliman
 During the 60’s, the “Troll Doll” became a popular toy in the US and the UK. Short, naked, and with huge spiky hair, the trolls were a cure version of their androphagous ancestors.