Well, on the FanFiction site I'm A.A. Pessimal, but that was only so that I'd get to the top of any alphabetically-organised author list...
In my fan-created Discworld, I rather indulgently wrote myself in as my alter-ego Phillip Holtack, a man who is blasted out of Earth and onto the Disc... OK, a bit Marty-Stu, but the work "Slipping Between worlds" has been kindly, even well, received.
If I could be just about anything and anyone in or near enough to the published Canon, I'd quite like to be at the Assassins' School.... perhaps the young student Assassin who runs the illicit bookies, breaks the rules, and is severely shouted at by such as Alice Band... (masochism... but I''d like to meet her...)