Ambrosius, with Sir Didymus on his back.
Ambrosius is a cowardly Bearded Collie, and is the mount of Sir Didymus in Labyrinth. He seems to resemble Sarah's dog, Merlin (interestingly, in some versions of the Arthurian Legends the wizard Merlin is known as 'Merlin Ambrosius'). He has more sense than his master.