Guy is a non-canonical character who was created for the adaptation of The Manhood of Edward Robinson, the tenth episode of the Thames Television series The Agatha Christie Hour. He is one of two men with Poppy at the bar of the Tantalus Hotel at the time when Edward Robinson arrived. See the article under Poppy for details.
This character does not exist in the original story.
The part of Guy is played by Rupert Everett.