Hans Castorp is the main character in the novel "The Magic Mountain" by Thomas Mann. He is a young German engineer who visits a sanatorium in the Swiss Alps for a short stay but ends up remaining there for several years. Throughout his time at the sanatorium, Hans encounters various patients and intellectuals, which leads him to explore themes of time, illness, and the nature of existence. His experiences reflect the broader cultural and philosophical questions of early 20th-century Europe.