Donald Duck

Donald Duck was, depending on whom was asked, either a cartoon character or a real performer.

Appearing in Clock Cleaners
When the Fourth Doctor hosted Disney Time, he asked a passerby if he knew where Mickey, Donald and Goofy were. The passerby identified them as "Disney toons." The Doctor, however, then spoke of how he once knew Mickey Mouse personally. He then introduced a clip from the Disney cartoon Clock Cleaners, which featured the trio. In the clip, Donald was first seen washing his mop in a bucket of water, before dancing and walking over to a ladder while singing "Hickory Dickory Dock", before climbing up onto the mainspring despite the warnings to stay off of the spring. He then proceeded to mop the mainspring before the mop became stuck in it, causing him to attempt to free the mop. After managing to get it out, the mainspring broke, leaving him in the middle of it, as noticed by Mickey Mouse.

He used his hammer to attempt to fix the mainspring, but every time he hammered it down, another part came back up. The third time this happened, the section of the spring which stuck out prodded him, causing him to have an argument with it, being surprised when it first replied to him. Ultimately, he became frustrated with the spring and threw his hammer at it, only to have it launched back at him, firing him into a mechanical cog. He was thrown back and forth by the cog, before falling out, with his head still moving. After holding his head in place, his body continued to move; after holding his legs in place, his pelvis continued moving; after holding this in place, his legs began to move. He attempted to resolve this by holding all of the aforementioned parts of his body in place, but his hat continued moving. (TV: Disney Time)

Other references
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)

Donald was featured on a postcard alongside Mickey Mouse stuck to a refrigerator in Rani Chandra's house. (TV: The Mark of the Berserker)