Walter the Worm

Walter the Worm was a sentient worm that lived on Earth.

At some point in the 20th century in London he was in a hole and expressed discomfort when Susan Foreman played pop music on her radio loudly. When the pop music repelled the approaching Cybermen back into their spaceship he expressed happiness, as did Susan and the First Doctor. (PROSE: Dr. First)

At one point he was chased across a hillside by Daleks. Somehow he escaped extermination. (WC: The Daleks Chase Walter the Worm)

At some point in the 21st century he was sitting in a hole when the Fourth Doctor and Sarah Jane ran past, running from a group of Daleks. Shortly after this, Walter too, left his hole to flee from them. Once again, he narrowly escaped death. (PROSE: Dr. Fourth)

Later, he was sitting at the top of a ravine in a wood. The Seventh Doctor had climbed the ravine from the undergrowth below and was peering over the rock face at Walter and the figure behind him. The figure was in fact. By the time the Master had announced his presence and had started advancing towards the Doctor and Ace, Walter was gone. (PROSE: Dr. Seventh)

Behind the scenes
Walter the Worm is a character from the original run of Mr. Men books who regularly made small cameos, often simply sitting in a hole.