Robert Siddaway is a non-canonical character created for the 1993 film adaptation of The Case of the Missing Will in Series 5 of ITV's Agatha Christie's Poirot. He is the son of John and Sarah Siddaway. Robert is also the childhood friend of Violet Wilson, the ward of Andrew Marsh. At the time of the events in the episode, Robert is a second year undergraduate at Cambridge University and he and Violet have a romantic relationship.
After the death of Andrew Marsh and the disappearance of his will, Sarah hinted to her son that he might be Andrew's son and so able to lay claim to the estate. Robert and Violet consulted Phyllida Campion who suggested that they go see Hercule Poirot about it. Phyllida knew, of course, that this speculation was groundless. In the event, nothing came of this. Robert and Violet did go to see Poirot but by this time, they had become disillusioned with how the case was proceeding, especially after a family friend Dr Martin Pritchard was arrested by the police on suspicion of murdering Andrew Marsh. Robert planned to forego his studies at Cambridge and he and Violet planned to emigrate to the United States. Poirot however managed to convince them to give him more time to solve the case.