Wikipedia reminds us about the significance of red shirts in science fiction television:
A redshirt is a stock character in science fiction whose sole purpose is to die violently soon after being introduced. Redshirts are a plot device used to indicate the dangerous circumstances faced by the main characters at the start of a narrative.
The term comes from the popular American science fiction television series Star Trek. In this series, characters wear shirt colors defining their station and/or area of expertise. In the original 1966 series, a person wearing a red shirt was a member of the Engineering or Security department. Security officers had a habit of meeting tragic ends in nearly every episode.
Typically, an away team would consist of Kirk, Spock, McCoy (all main characters who stood zero chance of dying) and one never-before-seen red-shirted ensign, who would invariably be dead by the end of the mission.
Pictured here is the original “red shirt” death from Star Trek. The episode was “Obsession”. (No, I do not know that off the top of my head! I read it in Wikipedia!)