Xylok

The Xylok are a mysterious race, the only example being Mr Smith.
 * It can only be guessed what the biology and technology of the Xylok is like from the prime example, Mr Smith.

History
When a Xylok ship crashed into the Earth in the Distant past, they were all trapped in the planet. When Krakatoa erupted, one Xylok escaped. Sarah Jane Smith was sent a crystal that had somehow made a conection with the trapped Xylok. This crystal bonded with computers eventually becoming Mr Smith. He helps Sarah Jane on many occasions but belives he has a purpose and tries to crash the Moon into Earth to free his trapped form. This was stopped with a virus.

Mr Smith is then split off from the trapped Xylok and continues to work for Sarah Jane. (SJA: The Lost Boy)