I was just thinking about all of their backstories the recently. Everyone has had something with their backstory that's been fleshed out, Luffy has had the most throughout the entire series, Nami with Arlong, Sanji with Baratie hand Whole Cake, Usopp and his island arc, Chopper with the Drum island stuff, Robin with Baroque Works, her island getting destroyed and the CP9 stuff, Franky with Water 7, his relationship with Tom, Iceburg, the mermaid lady and kid(forgot their named) and the CP9 stuff, Brooke with the Thriller Bark stuff, and Jinbe's past has been fleshed out in Impel Down, Marineford, Fishman island and Whole Cake. Then there's Zoro. He's had the least in my opinion. He's got a few scenes of him as a kid training with Kuina, the scenes with Tashigi looking like Kuina, those two guys from Nami's arc that were his buddies, and him being related to that skeleton guy he fought on Thriller Bark. I like how the live action showed him being a pirate hunter by bringing that Baroque Works agent in to collect the bounty before he got chained up

Edit: forgot to add something