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, which featured Donald, was also shown in the story.