Someone who gives up their free time to help build an enormously useful internet project called Wikipedia that provides loads and loads free information about any topic you could think of, accessible to everyone who has internet access. Wikipedians are often critised for not having a life by trolls who copy their work when they're supposed to write about something.
<troll>: what did u do yesterday at 6 oclock?
<wikipedian>: I finished my work on the article x on Wikipedia
<troll>: omg omg ur a faggot i played pc games wif my friends coz im cool get a life <goes to Wikipedia and copies an article so that he wouldn't have to write an essay>