Ta-dah! I’ve been meaning to make this ever since I found this site.
This generator will spit out a list of 6 attributes that will expand on your Sims; 2 for appearance (roughly grouped into “things they can control” and “things they can’t”), 2 for in-game effects (“behaviour” and “preferences”), 1 personality quirk that can help influence how you see/write that Sim outside of gameplay, and 1 random favourite.
I made this with pre-existing Sims in mind - so theoretically any existing Sim could be modified to fit the results without having to change their genetics, facial structure, personality points or aspiration - although some require custom content or some minor tinkering in SimPE (like for height). I recommend using the generator when your Sim ages up to child so you can start forming an idea of your Sim’s personality. That being said, you could use it to make Sims in CAS too.
It’s designed for Sims 2, but I’m sure TS3 players could use it, it’s just a couple of the fields would cross over with traits/moodlets.
There are 41 different possible outcomes in each of the 6 fields so you should get pretty varied results!
I hope someone else finds this useful! :)