Mine is mostly my first name.
For the rest, many years ago I was in London and went to a night of mixed entertainment at some pub somewhere (I was not yet a live music person, so it was anomalous, and I don't remember much about it). There was some singing, and some light panto, and some stand-up, and one pair of guys did an improv bit which ended with them improvising a heroic poem, taking a name for the hero and a couple of items from the audience.
I was volunteered to be the hero, and so their saga ended (after dragons, maidens, wizards, etc.) with something like:
And so it is fitting the stories are told
Of the heroic adventures of Linus the Bold!
It's a particularly clever bit of improv, because it sounded incredibly impressive - it went on for several minutes, all in supposedly-spontaneous improvisational rhyme - but in fact all you have to do is memorize this long rhyming poem and then slot in the names and items supplied by the audience. Anyway, it makes a great user name.