Characters as Device

"You mere device," he gnarled. "You platitude! You Golux ex machina!"

— The 13 Clocks

In service to the plot, characters are given these roles, sometimes making them just plot devices with lines (although, like devices, characters can and do get upgrades).

These devices can also be viewed as component parts from which more complex, realistic characters can be built. Television production usually means churning out episodes as quickly as possible to meet looming deadlines, so we see a goodly number of these on television shows.

Contrast Characterization Tropes, where the plot serves the establishment of the character.