Arbitan

Arbitan was the Keeper of the Conscience of Marinus and father of Sabetha. He was also a scientist.

Arbitan guarded the Conscience from the Voords who were trying to capture it. However, he foresaw the need for the Conscience to be used and so sent several people out to fetch the four missing keys, including his daughter Sabetha, Altos and Eprin. None of them returned. When the First Doctor, Ian Chesterton, Barbara Wright and Susan Foreman arrived on the island they managed to find the building which housed the Conscience. Everyone got taken inside by Arbitan, and he stabbed and killed a Voord who was about to kill Susan. Not long later, a Voord attacked him and the two had a brief struggle until Ian walked into the corridor and saw what was happening. He punched the Voord who fell against the wall and Arbitan activated a control, causing the wall to open and the Voord to fall into acid. Arbitan then released the Doctor, Barbara and Susan, and he explained about the Conscience to them. He wanted them to find the keys for him, but they refused. Before they could leave Marinus, Arbitan threw up a force field, preventing them to get inside the TARDIS. He gave them two choices: either they could search for the keys, or they would remain on the island with out food or water. This blackmail gave them no choice and they accepted. Arbitan gave everyone travel dials with the right course on them for the locations of the keys. Shortly after they left, Arbitan was stabbed and killed by a Voord who had been hidden nearby. (TV: "The Sea of Death")

Yartek, the leader of the Voords, pretended to be Arbitan by dressing in the Keeper's robe, keeping in the shadows and hiding his features beneath the hood of the garment. (TV: "The Keys of Marinus")

By the time the Doctor revisited Marinus several centuries later, Arbitan's people had adopted his name as that of their species. (PROSE: The Fishmen of Kandalinga)