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.
Characterization Marches On, where a character undergoes significant changes in characterisation early on in the work due to creators changing their minds about them, and the original characterisation is simply forgotten about.
The Heel–Face Turn, Face–Heel Turn and Morality Adjustment tropes rely on character development to make this a believable turn of events.
Protagonist Journey to Villain is when an otherwise good character develops bit by bit into a villain.
Hidden Depths has a character develop in unexpected directions. It can also describe a 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.
A Character Check can help steer a character who developed too far from their original character back into being themselves, or remind the audience that they still are the same person they used to be no matter how much they've changed.
When combat factors into their development, then they Took a Level in Badass.
A Jerk-to-Nice-Guy Plot is a specific form of character development where the character learns a lesson and takes a level in kindness.
Conversely, sometimes a nice character gets disillusioned and takes a level in jerkass or cynicism.
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.
