|Appearance:||The Doctor Trap|
He claimed to be a human student who came from Earth in 1973 when he is attempting to gain Donna's trust and trick her into assisting him, but the Doctor was not able to confirm this.
He was an expert sportsman who hunted and collected rare creatures, including Mmtefl Beasts, Zargregs, Moogs, Daleks, a Raston Warrior Robot and even an Eternal, all of which he has killed and placed on display in a large trophy room. His ultimate trophy was to have been the Tenth Doctor, the last Time Lord, and he forcibly recruited The Endangered Dangerous Species Society to hunt the Doctor for his amusement. His plan fails when the Doctor switched places with Baris, gained access to Planet 1's computer systems and with the assistance of Planet 1 itself was eventually able to escape. Sebastiene was last seen after Planet 1 decides it didn't need him anymore and he promptly with the help of the Doctor, Donna and Baris, destroyed a large part of its northern continent using explosive decoy robots. He tried to hold the Doctor hostage on the condition that he take him from Planet 1, but the Doctor refuses. Sebastiene is then attacked by the last remaining hunter, the Carpalian Witch, and is last seen fighting it off with his sword alongside Baris.(PROSE: The Doctor Trap)