Which character was Catherine Willows' father on CSI?

Sam Braun was Catherine Willows' biological father on CSI: Crime Scene Investigation.

Catherine grew up believing that her father was absent from her life. Sam Braun, a powerful Las Vegas casino owner and a longtime family friend, had been present around her without revealing their true relationship. The truth emerged when Catherine compared Braun's DNA with her own during the episode "Inside the Box."

The revelation created an uncomfortable connection between Catherine's professional work and Braun's business empire. Braun was wealthy, influential, and occasionally involved in cases investigated by Catherine and her colleagues. Catherine had ethical concerns about accepting his help and money, but their relationship gradually became more personal after the truth was exposed.

A common mix-up is confusing Sam Braun with Catherine's ex-husband, Eddie Willows, who was Lindsey's father. Braun was Catherine's biological father, while Eddie was her former husband and the father of her daughter. Sam Braun was later shot and died in Catherine's arms during the seventh season episode "Built to Kill, Part 2."