Don is one of my favorite premades. I didn't care about him until I played with his character. He actually has an interesting personality. He never flirts with anyone autonomously, even if he's supposed to be a serial romantic, but if I have my Sim to date him he's very flirty and almost obsessed with her.
I first played the serial romantic aspiration with him and made him have babies with every woman in the world, whether they were married or not. I was still a noob on playing Sims back then and I didn't know about culling and most of his children that he had with townies got culled. It was upsetting because he was an excellent father. I ended up deleting the save.
On my other save he's currently married with my Sim and they have a daughter. He was first just a "friend with benefits" with my Sim. She's a gardener and she needed some fun when she'd worked all day. She used to invite Don over and they woohood few times per week. Then Don started appearing on her door every night, he was very obsessed and I thought maybe they should really start dating. They did and one day she got pregnant. Don was again very devoted father and I decided to get them married. I got rid of his noncommittal trait eventually and changed it to family-oriented trait because it seemed to suit him much better. He's a detective and they live in Strangerville. He's working on solving the Strangerville mystery.
On another one my current save he's a vampire. My evil vampire queen Evilia Doom had a child with him and she turned him into a vampire. They live together now, but they're not married and I'm not sure if they ever will be. Evilia just wanted him to be close to their son and protect him.