Simon Mortmain is a fictional character from the novel "I Capture the Castle" by Dodie Smith. He is the son of the castle's owner, Mortmain Castle, and is portrayed as a thoughtful and introspective young man. Simon is known for his artistic aspirations and his deep connection to the castle and its surroundings. Throughout the story, Simon develops a romantic relationship with the protagonist, Cassandra Mortmain. His character embodies themes of love, ambition, and the struggles of growing up in a changing world. Simon's journey reflects the challenges faced by young adults as they navigate their dreams and relationships.