Some characters have proper character development, where they go through things that make sense to the overall character. Others, on the other hand, end up being written so badly that they become unrecognizable. It can result in the character being damaged beyond repair and hated by the audience. Here is a web page explaining this trope: https://tvtropes.org/pmwiki/pmwiki.p...cterDerailment
Some examples: Cyclops in X-Men, circa 2003-2016. Also, Felicity Smoak from Arrow.