Via YouTube, a stunning find for this Peter Cook megafan: a newsreel from the filming of the Cook/Moore classic "Bedazzled" (early in the filming, I think). It shows a side of Cook's characterization that I never realized; apparently, he initially envisioned the Devil as a variation on his gloriously stultifying E.L. Wisty character.
In a strange and deep way, I think Cook's performance here — when he manages to stay in character — is closer to the actual Devil than any other portrayal of Lucifer that I've seen. Many of his answers are theologically astute, to the point of being Augustinian. It's said that he really did get into the character, even portraying the Devil in a theological debate at a London church.
I don't know about you, but I died when Cook likened his serpent outfit to something by Courrèges.
If you've never seen the film, here's a highlight: