Sophie Stone

 played Cass in the Doctor Who television stories Under the Lake and Before the Flood.

Just like her character, Sophie herself is deaf from birth, and did not develop any speech until much later in life. She was the first ever deaf person to be trained at and accepted into the drama school, in London.

She was also the second deaf actor to appear in Doctor Who, after Tim Barlow in Destiny of the Daleks.

In her 2015 Doctor Who Extra interview, accompanying the first episode in which she appeared, Sophie spoke, both out loud and in British Sign Language, about some of the challenges of working as a deaf actor, and about her gratitude for being able to play a deaf character who isn't vulnerable, but intelligent and strong.