My favorite droid was always R5-D4. It was an astromech, but it just was a little off. It seemed maybe older-looking to me as a kid. I saw a photo a while back of R5-J2, one of the black Imperial droids from ROTJ, and I couldn't stop thinking about it. I built t with my son who was 9 at the time, and I let him pick the colors, and I love this particular detachment, so I decided to name him after it. Since then we have also built an R4 dome to change out for this guy so that he often becomes R4-V9.
We then built a second droid, R2-A6.