Doctor Who: 10 Best NuWho Guest Stars Ever

10. Colin Salmon

Despite being a solid character actor, Colin Salmon may not be the first name that comes to mind when thinking either of a famous British actor or a Doctor Who guest star. However, his role in Silence in the Library/Forest of the Dead is extremely underrated.

He played Doctor Moon, a psychiatrist for a young girl called Cal, who turned out to be essentially the anti-virus programme on the library's futuristic central mainframe where the young girl lived. He never actually met the Doctor himself, but that didn't mean he didn't leave an impression.

While he was arguably overshadowed by the first appearance of River Song, Salmon's calm and controlled performance sets off the sense that not everything is quite right. Especially when it comes to his delivery of, "Then... you forgot", he oozes a sense of being sinister while also trying to help. Additionally, there's an element of unspoken authority even behind the minor deference to his 'clients'.

All these various aspects contribute to what is a fantastic performance and Dr Moon is central to how the episode works, creating the  ominous sense to the overall mystery behind the plot.