"You have the opportunity, here and now, to choose. To become something greater and nobler, and more difficult than what you were before. The universe does not offer such chances often, G'kar."—Nameless Narn, Babylon 5 -- "Dust to Dust"
Character development is, by definition, the change in characterization of a Dynamic Character, who changes over the course of a narrative. At its core, it shows a character changing. Most narrative fiction in any media will feature some display of this.
While the definition of "good" and "bad" character development is subjective, it's generally agreed upon that good character development is believable and rounds out a well-written character. Bad character development leads to the feeling that someone is manipulating the events to their own whims, or even reduces the character's believability.
There are many sub-tropes that take place due to this trope, some of which include
- The Coming of Age Story is centered around this trope in the context of growing up.
- Darker and Edgier and Lighter and Softer can either deepen a character or round out unnecessary roughness. They can also turn them into a pile of mush or make them an unsympathetic jerk.
- Similiarly, despite the negative connotations in the name, Badass Decay can soften a previously harsh character. Or it can ruin an awesome character.
- Flanderization is when a character has a quirk or personality trait that slowly becomes their only defining characteristic.
- Heel Face Turn and Face Heel Turn rely on character development to make this a believable turn of events.
- Hidden Depths has a character develop in unexpected directions. It can also describe Flat Character turning into a Rounded Character.
- Out-of-Character Moment may be a positive or negative example, generally steering a character in new directions without wholesale Character Derailment.
These are hardly the only examples. The Evil Twin of Character Development is Character Derailment. Beware this trope. To see the opposite of this trope, see Static Character. See also Flat Character and Rounded Character. Compare Hidden Depths, where something is revealed that was true all along, but would not have been visible before.
The oldest form of this is the moral decay of the Anti-Hero, as in Shakespeare's Macbeth or Coriolanus. In each case the protagonist's growing vices are timidly concealed at first but then openly displayed. A fascinating reversal of this occurs in Schindler's List - at first Schindler claims he is only saving people because he needs them for his business. By the end he is openly losing millions. His inversion of moral decay goes from an intention to get rich by exploiting slave labour, to crying over not saving one more person.