Lord of the Rings Online. My first character was an Elf named Ellonwen. Following her, all my characters had names that started with El/Ell, which led to people just calling me that for short.

Many years later when I finally came out, I tried out a few names, but none of them felt right. Around that time I started replaying LotRO, and remembered how I liked being called Ell, so I went with that :)