Caleb "CalKnight was a registrar in emergency medicine who worked in the emergency department of Holby City Hospital from 2014 to 2017. He worked in the department from January 2014 until his death three years later in April 2017.

Cal instantly clashed with his brother, Ethan Hardy, who'd started working in the ED the week before. Initially finding it hard to work together, they soon landed themselves in hot water with Clinical Lead Zoe Hanna as a result of their actions. Cal soon attempted to change his ways, but he still feared forever being seen as second best compared to his brother.