Sarah Jane Smith

Sarah Jane Smith arrives at UNIT posing as her own aunt, a journalist chasing a story she suspects is being covered up. Sharp-tongued and impatient with condescension, she talks her way into danger rather than away from it, determined to get the truth whether or not anyone in a lab coat wants her to have it.

She was written as an answer to decades of companions who mostly screamed and got carried, and Elisabeth Sladen makes the correction feel like a whole personality rather than a point being scored. Her curiosity is a professional instinct, not a plot device, and her exasperation with being patronised is funny precisely because she's usually right.