I've only got two pony ocs at the moment, but I don't think going over what inspired them would hurt so might as well
For my sona, Synth, his design was based a lot off of synthwave. The music was the most inspiration to make him in general, and I used images that go with the aesthetic when designing him. For his personality I mostly used myself, but exaggerated certain aspects so he's different enough.
For my second oc, Cyber, they were based off of a similar aesthetic, cyberpunk. Once again the music was the inspiration to make them, and I tried to use images to base their design around like I did with Synth - another inspiration was making a character based off of an aesthetic I liked again because it's fun and I think having my characters share that theme would be really interesting. I haven't decided much on their personality just yet, but I think I'll have them be quiet, calm, and collected - I don't think I got those traits from anywhere besides their design.
I rambled on for a bit on accident, but I think that sums it all up
Here's a little doodle I made of the both of them earlier in case anyone wanted to see them, Synth is on the left and Cyber is on the right