C. Norlander

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

Kate Stewart met Norlander when she arrived in the New Mexican town. The sheriff 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)