i am incredibly stuff at thinking out backstories, so most of my characters just have "A robot! Wow!" or some variant of.
there's an exception though. for an OC i haven't ever posted yet.
"this guy used to be a villain. with gigantic tanks and mechs a la Metal Slug, and raided stuff just for the fame and coolness factor. he wanted to be the tubular-est, with the most radical loving machines possible i mean stuff you're a villain and a gang leader you gotta REPRESENT
but then he got his stuff ruined by the robot girl squad and later reformed."