Most of that comes from careful brand management. Well-established franchise characters have lore bibles - established rules governing their appearance, behaviors, mannerisms, backstory, and other relevant details. These rules can clarify things about the character’s personality like “This character maintains a sense of honor and will not kill a helpless enemy in cold blood”, as well as “this character’s color palette includes these shades and may never wear these colors”. It is the purpose of these rules to define and establish what feels like the character and what does not. We developers then use these rules as constraints within which to create an in-game representation that conveys the desired experience.
The higher the commercial value of the character, the more important the managers of these lore bibles become. For new characters, the responsibility of maintaining character bibles usually fall to specific designers on the team - usually leads and seniors. For well-established franchise characters across multiple games, the bible is often maintained by a chief creative officer or creative director type. In the case of licensed characters like James Bond or Scooby Doo, there are often entire licensing teams dedicated to maintaining and enforcing the bibles.
Going from the set of rules to the actual gameplay experience is where people like me come in. We need to take a character outline and turn that into a set of game mechanics that, when played, feel like the character. This is exhibited through a variety of different aspects. Let’s run with the Wario example. Wario is heavy and weighty. Wario is selfish, gluttonous, and greedy. Wario is short-tempered and does not think long-term. Wario is willing to bend the rules in order to achieve his goals.
We can demonstrate his weightiness through his animations. When he changes direction, his large belly should probably continue with some inertia in the old direction. He should probably cause dust clouds to poof when he lands from a jump. His jump arc should probably be shorter than other, lighter characters. His facial animations should be very expressive - he should demonstrate his desires very clearly on his face when approaching game elements he likes - food, treasure, etc. This combination of visual storytelling and game mechanics as metaphor for aspects of his character combine to make the character feel like Wario to the player. We try to do this for all major characters. Most of the time we do a decent job. Sometimes we don’t. The bible enforcers try to keep us honest about it.
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