Trolls

Trolls are originally a mythical, cave-dwelling being depicted in folklore as either a giant or a dwarf, typically having a very ugly appearance.

A troll on the internet:

One who posts a deliberately provocative message to a newsgroup or message board with the intention of causing maximum disruption and argument

Internet troll

In Internet slang, a troll (/ˈtroʊl/, /ˈtrɒl/) is a person who sows discord on the Internet by starting arguments or upsetting people, by posting inflammatory, extraneous, or off-topic messages in an online community (such as a newsgroup, forum, chat room, or blog) with the deliberate intent of provoking readers into an emotional response[2] or of otherwise disrupting normal on-topic discussion, often for their own amusement.

This sense of the word "troll" and its associated verb trolling are associated with Internet discourse, but have been used more widely. Media attention in recent years has equated trolling with online harassment. For example, mass media has used troll to describe "a person who defaces Internet tribute sites with the aim of causing grief to families." In addition, depictions of trolling have been included in popular fictional works such as the HBO television program The Newsroom, in which a main character encounters harassing individuals online and tries to infiltrate their circles by posting negative sexual comments himself.