WarmTurtle started as my name in League. The story behind it is kinda cool, a bit long so bear with me.
In early 2011 players with "Riot" in their names had their names changed to "warmturtle<misc. numbers>". The alias I went by at the time was "RiotPirate" and having no idea who made League when I started playing, I saw no reason not to use it again.
Shortly after that said players were offered a free name change. I had gone back and fourth with an account specialist trying to find a name I liked that wasn't already taken. Finally I sent him a list and asked him to use whichever one off of it was available.
This is the reply I got:
Rivington, Mar-27 15:46 (PDT):
Hello Sasha,
The first name that worked in our database was WarmTurtle. Since no one was given this name during the name change you are now the official WarmTurtle.
Sincerely,
Rivington
Account Specialist