Vox (The Poison Planet)

The Vox was a creature that was devoted to protecting mustron V

When the 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 distroy the team of experts including the Doctor

the Doctor managed to turn the Vox against jennifer and continue to protect Mustron V