Sheriff of Nottingham

The  was an English noble and enemy to the outlaw Robin Hood.

He captured Maid Marian and imprisoned her in his dungeon. In one account he thought he had captured Robin trying to rescue Marian, but it was actually Ian Chesterton, who looked just like Robin.

He arranged to have Ian executed, but the First Doctor offered to show him the secrets of alchemy in exchange for Ian's release.

Nottingham later arranged for Susan to be executed, but fled in fear when Robin Hood's men and the villagers attacked. (PROSE: The Thief of Sherwood)

However a second account states that the Sheriff was later made into a cyborg, after an altercation with extraterrestrial robots. He led a plot to take control of the English throne, but was defeated by Robin Hood, who, during a sword fight, pushed him into a vat of molten gold. (TV: Robot of Sherwood)

Behind the scenes
A scene in Robot of Sherwood in which the Sheriff of Nottingham was beheaded by Robin Hood, revealing him to be a cyborg, was edited out of the episode's broadcast as it was deemed inappropriate in light of recent events in the news — namely, the beheading of two American journalists by terrorist group. However, the fact that he was a cyborg could still be seen when his hands were shown coming out of the vat of melted gold. The cut can clearly be seen in the finished episode when the tapestry behind Clara and the Doctor vanishes before Robin cuts the rope and rises to the wooden beams.