Shelob

Shelob is the name given to a large purple Arachnarok Spider by the Eleventh Doctor. She usually comes out to feast on some of the villagers and she has shown to be capable of speech. She does serve as the main antagonist for the first episode, but then an anti-hero in the Season 1 finale, where she helps the Eleventh Doctor, Merlin and Claire rescue Tyrant and the TARDIS from Davros' clutches.

In the first episode, Shelob appears after Claire tends to Tyrant's injury after he falls over. She chases the Doctor and his new friends until they hide. She later appears when the Doctor is debating about how the villagers are using their new helpline too often, leaving them defenseless when Shelob decides to feast on them. She is defeated when Tyrant gives the Doctor a Power Star, allowing him to throw her onto her back. Shelob then retreats.

In the Season finale, the Doctor and Merlin visit Shelob in her lair to try and get her to help them rescue Tyrant from Davros and a brainwashed Tenth Doctor. Shelob is hesitant at first, but when the Doctor offers her loads of food, Shelob agrees. Once Davros' castle is destroyed by Claire's sacrifice, Shelob returns to her cave.