For once, mine is pretty obvious! The "AE" gets tacked on when "Gwydion" is taken, no real reason for it - I'd just seen TitanAE and swiped it for a name I knew wouldn't be taken.
I chose Gwydion, however, as my first email account. I wanted to "surprise" a friend of mine by sending her puzzles to figure out my "true identity!". I chose "gwydion-3" as I loved KQ6/Alexander at the time - and I'd just bought her a copy - but I thought a direct reference would be too obvious. So "Gwydion" for his other name and "3" referencing which game he first appeared in.
...of course she knew all along it was me and never bothered with the puzzles. Never even played the game.

But I loved the name, so it stuck.
And it makes me feel quite appropriate to be a "Wizard's Slave", lol.