Dishonored

This last webisode for Dishonored's The Tales of Dunwall features Piero, a man who is a key figure in main character Corvo's story.

This episode, "In the Mind of Madness," takes place after the assassination of the Empress, and therefore during the game's storyline. Inventor Piero is driven to create the mask that Corvo wears.

Also check out the first and second episodes.