Pink Elephant

According to the Third Doctor, a Pink Elephant was a delegate at the Third Intergalactic Peace Conference. (TV: Frontier in Space) The Fourth Doctor explained the human mind to Davros by telling him a riddle about a pink elephant named Nellie. (TV: Destiny of the Daleks)

Behind the scenes

 * Since it was mentioned so briefly, it's unclear whether this was the species "proper" name or merely a descriptive name.
 * Culturally, a "pink elephant" is sometimes used to refer to illusions brought on by extreme inebriation.