Brand persona
A brand persona is the human character a brand adopts (its personality, values, and way of speaking), used to make communication feel like it comes from a consistent someone rather than a faceless company.
A brand persona answers "if our brand were a person, who would they be?" It bundles personality traits, values, and a way of speaking into a character that every writer can channel.
The persona is closely tied to brand voice (how the persona talks) and the brand archetype (the underlying personality pattern). A well-defined persona makes copy feel human and consistent, even when many different people write it.
To turn a persona into rules, see how to define your brand voice.