According to Wikipedia, a redshirt is
"a stock character in fiction who dies
soon after being introduced. The term originates
with fans of the Star Trek television series (1966–69),
from the red shirts worn by Starfleet security personnel
who frequently die during episodes."
Perhaps most of us relate to them…
One moment of glory,
That’s all that they get—
A spot in one story.
These hapless cadets
Beam down to the planet
With captain and crew;
We take it for granted
They’ll wind up as goo.
Now legends of Star Trek,
They’ve gone from dead ends
With too-tiny paychecks
To famed might-have-beens.