Personality
The brand characterized as a person
Imagining the brand as a person makes abstract brand values concrete and usable.
Brand personality is the set of human characteristics associated with a brand. When a brand is described as warm, confident, irreverent, or authoritative, those are personality attributes. Expressing brand personality as a character or persona makes it easier to test design, copy, and behavior decisions: would this character say that? Would they dress this way?
The failure mode is assigning personality attributes that are either aspirational (what we want to be) rather than authentic (what we actually are), or so vague that they apply to every brand in the category ('professional, friendly, innovative'). Personality should be distinctive enough to actually exclude choices, not so broad that it permits everything.