C. Norlander

"Norlander" was the name taken by a Zygon that had disguised itself as the sheriff of Truth or Consequences.

She met Kate Stewart when she arrived in the New Mexican town, and showed her the ashes of some of the residents after a Zygon invasion. Later, she revealed her true form to Kate and apparently killed her and took her form. (TV: The Zygon Invasion)