An important character is killed to launch a series.
It's a TV pilot, maybe pilot movie, and a cast of characters is introduced. However, there's always one character whose job is to fill a specific role, then die before the pilot is over. Reasons for death could be to show how serious a situation it is, to make room in the cast for a designated main character who takes their position, because they're the first bad guy seen and is killed for resolution within the pilot, or because their death launches the plot for the rest of the series. Compare Plot Triggering Death where the character starts out dead or dying. Also Death by Origin Story which takes place in the Back Story.