Gnasher

A black dog was a character in The Beano.

He appeared on the back of The Beano Summer Special 1981 with Dennis the Menace at Dolphinarium, a swimming pool. (TV: The Rings of Akhaten)

Behind the scenes
Although he was not named as "Gnasher" in TV: The Rings of Akhaten, he is named as such in the real world.

Gnasher was the pet dog of Dennis the Menace.