Arbitan

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

Arbitan guarded the Conscience against 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 found the building which housed the Conscience. They were taken inside by Arbitan, who also stabbed and killed a Voord who was about to kill Susan. Not long after, 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 from getting inside the TARDIS. He gave them two choices: either they could search for the keys, or they would remain on the island without 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 hiding nearby.

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)

When the Doctor visited Kandalinga, he learned from the Voord that Arbitan's people had adopted his name as that of their species. (PROSE: The Fishmen of Kandalinga)