Paine

Paine was an artificial being created by the Eleven as one of the workers on Phaiton, charged with operating a treadmill in the power-generation plant. He accidentally injured himself and was saved from the Orbs by the Eighth Doctor.

After being taken to the Eleven, Paine followed the Doctor's orders and took his sonic screwdriver to Liv Chenka and Helen Sinclair, telling them that they should go to the TARDIS. Although Paine saved Helen from death, he was wounded by an Orb and died in Liv's arms. She destroyed an Orb in his name. (AUDIO: The Satanic Mill)

Behind the scenes
The Eleven refers to Paine as a new companion of the Doctor, something that the Doctor does not deny.