Kadonnut means 'disappeared' or 'lost' in Finnish. I first started using it as an away-nick in IRC but eventually I quit changing nicknames there. This happened around 2010-2011 I guess. I'm using the same nickname on pretty much every online platform I am on, and in case the nick is already taken before me, I switch the o to 0 - it has been enough so far. Rarely I've used the German equivalent of the word, 'Verschwunden'.
A bit like building a brand of me around the nickname even though there's nothing 'brandworthy'.