Donald Duck

At Castle Extremis, Martha Jones jokingly introduced the Tenth Doctor as "Doctor Donald Duck", after he in turn introduced her as "Martha Mouse". (PROSE: Martha in the Mirror)

Behind the scenes
Donald was also mentioned in the invalid Disney Time 1975, in which the Fourth Doctor asked a passerby where he could find the duck, as well as Mickey Mouse and Goofy. The passerby explicitly identifies Donald as being a "Disney toon". Nonetheless, the Doctor goes on to talk of the characters as if they were real individuals. The Disney cartoon Clock Cleaners, which featured Donald, was also shown in the story.