Caleb "Cal" Knight is a fictional character from the BBC medical drama Casualty, played by actor Richard Winsor. He first appeared in the series twenty-eight episode "Brothers at Arms", broadcast on 18 January 2014. Winsor had previously auditioned for a role in Casualty's spin-off show Holby City. Producers were impressed and recalled him to read for the part of Cal. Winsor's casting was announced alongside George Rainsford who was hired to play Cal's brother Ethan Hardy. The pair had to pass a screen test together as producers were looking for a strong sibling chemistry. Cal's role in the show is a Specialist registrar in emergency medicine. He was originally introduced as a locum. The medic is played as a lothario and womaniser type character. He can manipulate those around him with charm to better his career. Writers gave Cal a backstory detailing the difficult relationship with his father and brother. Despite having the same parents Cal and Ethan had different upbringings, which sets up a sibling rivalry. Their relationship has been important in the development of both characters. Executive producer Oliver Kent has called the character consistent because when faced with trauma, Cal gets drunk, sleeps with women and makes a fool of himself.

The twenty-eighth series of Casualty began airing on BBC One on 3 August 2013, one week after the end of the previous series. This series consisted of 48 episodes, the highest episode order since series 24. The series concluded on 23 August 2014.