Hey Riot, when making a champion, how do you decide their appearance?

I know you guys sometimes take inspiration from shows/movies/other games/legends and folklore/etc. but excluding those, Is there a certain process you use? Like for example, why does Bard sorta resemble Santa? was there anything holding him back from being a Yordle or an angel like Morgana and Kayle (oooohhh what if he is actually XD). Or why was Rengar made to be a giant kitty? Or Shaco a demented clown? Or Ryze being blue? What was/is the process behind making certain champions look the way they do. Is there even one or do the designers make it however they want?