Zombieman

The Trooper (also known as the Zombieman) is a marine who has been turned into a zombie during the invasion of the UAC bases. He appears as a green-haired man in bloodied utility uniform, carrying an assault rifle.

The Doom instruction manual says:
 * Just a few days ago, you were probably swapping war stories with one of these guys. Now it's time to swap some lead upside their head.

The trooper first appears on E1M1: Hangar (irrespective of skill level).

Combat characteristics
The trooper attacks by firing a single bullet, which is slightly less powerful than the player's bullet. He is arguably the least dangerous enemy in the game; no other monster (excepting Commander Keen) has a lower movement rate, hit point total, or average damage per shot. When killed, he drops an ammo clip containing 5 bullets (10 on I'm too young to die and Nightmare!).

Tactical analysis
A healthy player should never back down from a single trooper, although large groups can create a slow, steady drain on the player's health during the time it takes to kill them all (as with MAP09: Stronghold or PET2.WAD from Maximum Doom). His aim is somewhat unreliable even at medium range; consequently, he often finds himself outgunned at long range, even by a player with a pistol.

The trooper's low rate of fire and damage capability make him a rather weak contributor to monster-monster battles. Attrition among a crowd of troopers is generally slow, and distraction of larger monsters minimal.

In a stock level, the first few rooms typically contain a preponderance of former humans. Unless the player's primary goal is to reach the exit rapidly, it may be wise to carefully collect the ammo clips before proceeding; one never knows when 20 or 30 extra bullets will be the difference between clearing a room and being cornered by two chaingunners.

Appearance statistics
The IWADs contain the following numbers of troopers: