Mr. Tumnus is a faun in The Chronicles of Narnia books written by C. S. Lewis, primarily in The Lion, the Witch and the Wardrobe but also briefly in The Horse and His Boy and in The Last Battle.

Lewis wrote that the first Narnia story, The Lion, the Witch and the Wardrobe, all came to him from a single picture he had in his head of a faun carrying an umbrella and parcels through a snowy wood.

When Lucy and her siblings subsequently come to Narnia some time afterwards, they find that Tumnus has been arrested by Maugrim, Chief of the White Witch's secret police, and is awaiting trial on a charge of high treason which involves harbouring spies and fraternizing with humans.

In The Horse and His Boy, Tumnus appears as a royal adviser to the four Pevensie monarchs (fourteen years later, according to Lewis's Narnian Timeline).

He devises a plan for escaping from Calormen, thereby saving Queen Susan from being forcibly married to Prince Rabadash, and the other Narnians, including her brother Edmund, from certain death trying to defend her.