Smudge

 was Susie White's pet cat. He loved cheese and if he smelt cheese sandwiches, he always came running to Susie. In the 21st century, Smudge had gone missing, and as a prank, Miss Chief told Susie that she was never going to see him again. After Smudge had turned up, Miss Chief unwittingly sent him back him time when she took the Twelfth Doctor and Clara Oswald back in time to the 17th century to save Agnes Leech's life. Clara did this by convincing the mob that the Witchfinder General Matthew Hopkins was a witch, with Smudge as his familiar, when she hid a cheese sandwich in Hopkins' pocket and had Smudge "greet" Hopkins. Clara later brought Smudge aboard the TARDIS to bring him back home. (COMIC: Witch Hunt)