From Quake Wiki
The Enforcer is the brute of the military base maps. You can tell them apart by their beefier build, helmets and backpack. Wielding a laser cannon with perfect aim, they fire in two shot bursts, ensuring that you have to step quickly to avoid harm. On death they will drop a backpack containing five cells.
Enforcers are the only Quake monster showing Earth human intelligence, as some of their sounds bear a strong resemblance to English words, typically used by guards of any sort. This suggests that in their strength, they were less assimilated as a whole by Quake's forces, and thus retained a bit more of their minds.
Interestingly, their uniform bears a strong resemblance to the Biosuit, which can be used as rationale for their underwater excursions in The Sewage System, though the Grunts doing the same are a mystery. Easy to be knocked into a pain frame, and lacking a melee attack, Enforcers are generally best dealt with by the Double-Barrelled Shotgun as the normal one would be wasteful of shells, but the Nailgun can work well on a group.
Their projectile can also be found as an option for the trap_shooter entity, which can be seen used to an extreme extent in the first level of Beyond Belief where a tight cluster of them act as a security system to prevent the player from passing. Beyond Belief also modified the Enforcer to drop only two cells on death, making them less of a boon to the player at a later point upon finding the Thunderbolt.
monster_enforcer is the entity for placing Enforcers in a level.
|targetname||The targetname of the Enforcer. When triggered, the Enforcer will wake up if inactive.|
|target||The targetname of the entity to be triggered when the Enforcer dies.|
|killtarget||The targetname of the entity to be removed when the Enforcer dies.|
The monster_enforcer entity supports the following spawnflags:
|1||Ambush||The Grunt will not wake up from seeing other monsters wake up or hearing sounds.|
It also supports the standard spawnflags for difficulty and deathmatch presence.
|256||Not on Easy||The Enforcer will not spawn on Easy difficulty.|
|512||Not on Normal||The Enforcer will not spawn on Normal difficulty.|
|1024||Not on Hard||The Enforcer will not spawn on Hard difficulty.|
|2048||Not in Deathmatch||The Enforcer will not spawn in Deathmatch mode.|
This is the format used by TrenchBroom and Worldcraft. Note that the model(...) parameter is not supported by Worldcraft. This does not include the Monster base class definition, which is also required.
@PointClass base(Monster) size(-16 -16 -24, 16 16 40) model(":progs/enforcer.mdl") = monster_enforcer : "Enforcer" 
This is the definition format used for most old Quake editors, including the original QuakeEd.
/*QUAKED monster_enforcer (1 0 0) (-16 -16 -24) (16 16 40) Ambush */