The chronicles of my avatars...
The first one worth mentioning was the Hufflepuff crest:
The Hufflepuff crest was chosen because, well, I'm a Hufflepuff. And at the beginning of my activity here, I was only active in the harry-potter tag, and so my avatar reflected that.
Around Winter Bash 2016, I changed it to an image of Mr. Spock:
I needed a head to put a hat on, and Spock seemed like a good idea on a site dedicated to Science Fiction and Fantasy. Also, something something smart something something answer questions.
After a while I then changed it to fit my username:
(My username being "Mithrandir", the name that the Elves call Gandalf.)
I then felt a pull to the Dark Side and updated to an image of Sauron:
I stuck with Sauron for a while. Then out of fear of becoming a Ringwraith...
...it was changed to a picture of Arwen Undómiel.
(This image is a screenshot from the poster for the The Return of the King movie, taken from a YouTube video playing the soundtrack.)
And to switch to a different universe...
Screenshot from a YouTube upload of the song "Whatcha Doin'?" from the episode "Roller Coaster - The Musical".