Sandcars

When Figment found the Doctor's TARDIS, he remarked, "How terribly nice of Officer Sandcars." Figment wondered what he looked like. (POEM: Beforwards) By sunset the same day, Figment had still not met him. (POEM: Afterwords)

Behind the scenes
The non-existent character of Sandcars is actually a result of Figment misreading the phrase "OFFICERS AND CARS" on the TARDIS.