I joined in 2007, not to BE anything, but to hang out and do stuff in a virtual world with friends I didn't get to see much in the real world because of distance or other reasons.
I found a load of clothes that vaguely matched what I would wear in the real world and had fun with my friends, who were also avatar versions of their RL selves. I got a bit of mainland where there were some sci-fi related things around, and I lived in a space station there. I played around with building stuff and making basic clothes. I had a couple of jobs.
I didn't log in for a few years and came back, I think 3 or 4 years ago. A lot had changed. Me walking about with my system body and system/prim clothes while everyone else was all mesh! The avatar I used to be proud of looked like a cartoon next to everyone else. So I soon upgraded how I looked!
My RL friends, and the early friends I made inworld, have all left SL now so I'm no longer very sociable in it. I just decorate homes and play with clothes really. And do stuff/explore sims on my own when I feel like it. I'll talk to people in local in the more sociable areas but I don't tend to have actual friends. I don't have time to commit to building, content creation etc although I do sometimes take the notion to try, just for fun. (eg I did an online course on using Blender.) I can't commit to any particular day/time to be online so I don't do SL jobs anymore either.
I'm still predominantly human and wearing an idealised version of what I'd like to wear in the real world. (I don't dress quite like that in the real world anymore cos, unlike my avi, I aged and put on weight!! 😂 ) Just with a mesh body and well made clothes now. And a lot more of them!! Because one difference between RL me and SL me is that SL me loves shopping for them. 😳
I've played about with being non-human too. So far I've enjoyed being a mermaid best. But being a purple-skinned alien cyborg was fun too. As was being a tiny cat. I mean, you can change your species as easily as you can change your clothes so I do it when I feel like it! Definitely mostly just human though. But still always changing. If I could change my skin/hair/eye colour and body/face whenever I felt like it in RL too, I would!! (I do always tend to go back to black/purple clothes and hair though, just like in RL.)
I set up an alt a couple of years ago for practical reasons (mainly cos I needed to start a group for something) so have wandered around as a male on occasion, but I don't have any friends or anything on that account. I log in on it very occasionally when I have a practical reason for needing to, and I might then decide to go to a club or something as my alt for a short while. He has a freebie Altamura body and mostly freebie clothes picked up in the first 30 days from newbie areas. He doesn't look great, but I don't see the point in spending much money on an account I barely use.