What is a troll? How a useful word became a means of tagging any dissident

I am honest. He is a troll. They are a mob.

Trolling was once a pretty clearly defined behaviour. It meant a kind of puckish, Loki-like internet tendency, the kind of thing that in a world where offline was the only option would have been called satire or mischief. But the word ‘troll’ turned out to be exceedingly useful to people in power, both those with actual political power and those who have cultural and/or media power.