Vox (The Poison Planet)

The Vox was a creature that was devoted to protecting Mustron V. When the Tenth Doctor arrived on Mustron V the Vox tried to kill him but he was saved by Rachel Barlow. The Vox was then put under the control of Jennifer Arders who ordered it to destroy the team of experts including the Doctor, the Doctor managed to turn the Vox against Jennifer and continue to protect Mustron V. (DWAM: The Poison Planet)