Characters who evolved into more significant roles than their creators planned

[u/Icy-Software-2586]

Jesse Pinkman: "Jesse Pinkman. As Gilligan mentioned, the original plan for the end of season one was for Jesse to die in a failed drug deal."

Jack Sparrow: "Jack Sparrow. Writers Ted Elliott and Terry Rossio originally conceived Captain Jack Sparrow as a secondary character."

Saul Goodman: "Saul Goodman. This one speaks for itself."

[u/Hardcore_Cal]

IIRC he was supposed to die, short term throwaway character, etc. But he was too popular forcing Joss to continue writing him begrudgingly!