Cass (Under the Lake)

Cass was second in command of the Drum, an underwater mining facility in Scotland. She was also deaf, and used her good friend Lunn to translate her sign language.

When commanding officer Jonathan Moran was killed, Cass took charge. She led the remaining crew to the base's Faraday cage, where they would be safe from the ghost leader Prentis. Due to her sign language she was able to understand the silent words that the ghosts kept repeating. (TV: Under the Lake)

Behind the scenes

 * She is the first deaf character to appear in Doctor Who. Sophie Stone is not the first deaf actor to appear on the show, however.