O is for... Octavian

Father Octavian was an officer with the Clerics - a military-religious army of the 51st Century. His rank was Bishop, Second Class.

He led the mission to investigate the spaceship Byzantium, which had contained an escaped Weeping Angel. It had caused the ship to crash on the planet Alfava Metraxis. With the Clerics was River Song, released temporarily from prison to assist due to her knowledge of the creatures. She in turn had brought in the Doctor and Amy Pond. 

The Byzantium had landed in a labyrinth known as the Maze of the Dead, where the now extinct native population had once buried their dead. A human colony lay nearby, and Octavian was tasked with assessing and eliminating any risk which the Angel might pose to the settlers.

The Maze proved to be full of statues - and these turned out to be a whole army of Angels. The ship had been crashed here deliberately, so that its leaking radiation would reanimate the dormant Angels.

As part of River's timeline, he knew more about her than the Doctor did at this point, including the reasons she was incarcerated. At one point he pretended that he and River were engaged, so that he could accompany River and Doctor to the spaceship's flight deck.

Unfortunately, he was caught by a Weeping Angel and killed - though his death did buy the Doctor some time to deal with the creatures.

Played by: Iain Glen. Appearances: The Time of Angels / Flesh and Stone (2010).

• Best known for the role of Jorah Mormont in Game of Thrones, he has also appeared in a trio of the Resident Evil movies.
• The first TV role for the Edinburgh-born actor was as a suspect in an episode of Scots police drama Taggart.
• More recently he played Bruce Wayne in the Titans series.