Can someone write a short paragraph about how characters in stories are not always as they seem.

Certain characters in a story could seem one way but turn out to be different in the end. For example, a character could be nice throughout the entire story up until the turning point. This certain character could turn out to be the antagonist after all and we wouldn't suspect It or vice versa. The antagonist could turn into a protagonist towards the end. It all depends on how the character is developed and presented.

Give examples, people who actually harmed.