"Turret Runner" is a name used to describe certain Story AI in the TimeSplitters Future Perfect Mapmaker. They are AI that have been set up by the story-map making player to do something other than simply charge at and attack the player. They are designed to run away instead.
A Gun Turret is placed in the map for the AI to man. The AI must be a non-zombie, non-robot character except Deep Diver or Berserker Splitter, and must be armed with something other than a Baseball Bat. Ideally the AI will be set to be Stationary, Spawn and Wait, or have a very short patrol radius, not far from the gun turret. The gun turret must rotate 360 degrees and be spatially within ~2 grid squares of the AI. This isn't to say it needs to be within a 2-grid trek. It can be 2 floors down or up, but have as long a path to get to it as you want the AI to run. With this exploit working in custom missions, you can create objectives with civilians escaping or enemies fleeing which you must pursue.
When the turret runner sees the player, it will want to attack the player by using the gun turret. So off it will run to the turret, regardless of whether or not shots fired from the turret can actually hit the player, or whether or not they will encounter a locked door along the way, preventing them from accessing the turret. Since the turret runner must be armed with something to either fire or throw, they will fire at the player if they need to run towards the player on their way to the turret. If the player is not in their path, the player is usually safe from being fired upon.
Turret runners are drawn only to the first five gun turrets placed in a map, so the maximum number of spawned turret runners is five. A sixth gun turret placed in the map will not draw an AI, so the order in which multiple turrets are placed is important as to which turret draws which AI.
Turret runners are incapable of triggering an "AI spots player" trigger. Although they will "see" the player and run, they will run before the "spotting" is triggered, and once in running mode, they cannot "spot." In this regard, turret runners in running mode will be ignored by other AI who see them running; that is, a turret runner running past a waiting AI will not cause the waiting AI to be alerted to the player's presence, because the waiting AI would only be alerted to the player's presence if they see another AI who has actually spotted the player.
Inaccessible gun turrets can be used to create what has been called a "turret boss" Story AI. If a gun turret is within a potential runner's turret-perception range, but there is no path to the turret, the "turret boss" will stand in place and fire at the player. They are much more difficult to defeat than typical story AI because they do not flinch when fired upon with most weapons, and they do incredible damage to the player when armed with dual machine guns.