Who is the lunatic...

..in the prison hallways? The old timey guy. Did I miss something? I could not even find him in the credits for the Pilot which is all I have seen so far.

EDIT: never mind! I found the answer.
I dont consider this info to be a spoiler of any sort. I got it all off the BBC website. I think it helps to clarify things, not spoil them.

"Cream

A real life killer from the nineteenth century.
Fact title Fact data
Played by
Eddie Marsan

Thomas Neill Cream represents the bleakest aspects of the human condition – both in the minds of the killers that River investigates and in River himself.

He’s a constant reminder that the veneer of civilization is thin, and that we all have the potential for great darkness within us. He’s also a manifestation of the pull towards death, suicide and oblivion."

http://www.bbc.co.uk/programmes/profiles/3P1xnpVXlsFQ3cw1DGxvkbJ/cream

He was a right charming fellow!
https://en.wikipedia.org/wiki/Thomas_Neill_Cream