Gregory B. Rolf

In the short story The Adventure of 'The Western Star, Gregory B. Rolf' was an American film star and also the husband of a film star Mary Marvell. Some three years before the events in the story, he had met and had an affair with Lady Yardly when she had visited Hollywood. Subsequently he used some of her letters to blackmail her and obtained as payment her famous diamond "The Star of the East", leaving a fake diamond in its place. He later gave this diamond to his wife, creating a myth that there were two diamonds, east and west, both eyes of a Chinese idol. However some years later trouble arised. Lord Yardly considered selling his diamond, which worried Lady Yardly, fearing that the substitution would be discovered. Rolf realized that Lady Yardly might confess the whole story to her husband, and decide to solve it. In the story, Rolf contrived to steal his own diamond, disguised as a Chinese man, after first sending letters to Mary threatening that the diamonds must be returned to their rightful place as the eyes of the idol. He and Lady Yardly staged each a robbery. With the substitution stone gone, Lady Yardly's fears would be calmed down, Rolf would be safe, he could claim the insurance on the real diamond and still keep it.

Poirot saw through this plot and confronted him with the truth. According to Poirot, Rolf was "wax in his hands" and meekly surrendered the diamond.

Portrayals
Gregory Rolf was played by Oliver Cotton in the film adaptation of The Adventure of 'The Western Star' in Series 2 of ITV's Agatha Christie's Poirot. The portrayal is faithful to the original character except that Rolf was now a Belgian film star just like his wife, renamed Marie Marvelle.

In the adaptation, Rolf did not break down when confronted by Poirot. Rolf had been hoping to sell the stolen diamond to Henrik van Braks. Poirot managed to obtain the real diamond through the jeweller Hoffberg who was acting as the interdemidary between the two of them.

His wife Marie told Poirot that Rolf was "an idiot". He never believed he had any real talent and always felt the need to show what he was capable of.