Androvax

Androvax was an alien enemy of Sarah Jane Smith in the episode Prisoner of the Judoon.

Biology
The Androvax was a humanoid, reptilian creature with scaly skin and horns of various size protruding from its head and shoulders. It also had a long tongue which it could flail and retract at will. Androvax was a veil life-form which meant it could hide in the bodies of other beings and stun them as well. When it took over another being its tongue seemed to replace the one of the creature it had entered as shown when Sarah Jane was taken over and showed that she had a long reptilian tongue.

History
Androvax was the highest on the Judoon's most wanted list as he had apparently caused global destruction on twelve planets. He was caught by a Judoon Trooper, but during his transportation the pod he was in crashed on Earth. He knocked out his Judoon captor and escaped, taking over the body of a young girl. However, when Sarah Jane Smith detected him he revealed himself, stunned Clyde and entered her body instead. He then returned to her home in Sarah's body and instructed Mr Smith to self destruct, before proceeding to the Nanoform laboratories and instructing the microscopic robots to build him a ship.

Androvax was finally caught when Luke threatened to sabotage the ship, and ultimately stopped the Nanoforms from destroying the planet. The Veil was then sentenced to execution. It is unknown whether Androvax escaped from the execution or not.

His reason for destroying planets was jealousy, as his planet was lost. Rather like the Doctor, he was supposedly the last of his kind.

Behind the scenes
Androvax may return in the series 3 finale:The gift. this is in the previous series the first episode villians appeared in the last episode,I,e: the slitheen in series 1 and the sontaran in series 2.