The Locust Horde is the main enemy in Gears of War.
Emergence Day
The planet Sera had been inhabited by humans who had known peace. But, 14 years before Gears is set, the Locust Horde emerged, bringing death, destruction and turmoil to a once calm world.
Units
The Locust Horde is made up of several different units, most of which are playable in multiplayer.
Drones
Drones are the main infantry of the Locust Horde, and when free of armour, the easiest to kill. Occasionally, a Drone will wear a helmet, allowing him to survive one headshot from a Longshot.
Drones are normally armed with a Hammerburst or ocassionally a Boltok Pistol. Later in the game, Drones are also seen with Lancers.
Snipers
Snipers are the weakest of the Horde, but also the most accurate and most adept at using cover. Snipers never wear armour, so all weapons will kill in a few shots.
Snipers are armed with Longshot Sniper Rifles.
Grenadiers
Grenadiers are physically tougher than Drones, and more dangerous in close combat. Grenadiers don't wear helmets, so headshots from a distance are most effective.
Armed with the Gnasher Shotgun and Frag Grenades.
Elite Grenadiers
The Elites are slightly tougher and more intelligent than regular Grenadiers. They wear a bit more armour, making them harder to kill.
Armament is the same as Grenadiers, but a Hammerburst is also used.
Boomers
Boomers are the dumbest Locust around. They are huge, very tough, and armed with a Boomshot, a kind of rocket/grenade launcher.
Caution is advised. Up to three headshots with a Longshot are required to kill a Boomer.
Not playable in multiplayer.
Theron Guards
Very clever soldiers that often command Drones on the battle field. They are larger and much tougher than the Drones.
Armed with the Torque Bow, Boltok Pistol, Hammerburst and occasionally a Lancer.
Theron Sentinel
The highest ranking soldiers bred for combat. They are perhaps double the strength of a Theron Guard, though their armament is the same.
General RAAM
The greatest Locust General. Responsible for the deaths of many key COG figures, such as Adam Fenix, Marcus's father, and Lieutenant Minh Young Kim. He stands taller than any other soldier, and is approximately 10 times the strength of a Grenadier.
Armed with a Chaingun and a jagged sword for gutting Gears.
Berserkers
Berserkers are enormous creatures, deployed to take out entire squads of Gears. No Locust can control a Berserker, as seen in the cutscene before the chapter "China Shop" in Act 1, when the Drones that were meant to be watching the Berserker were all killed when the creature escaped.
Berserkers are only vulnerable to the Hammer of Dawn.
Not playable in multiplayer.
Nemacyst
Nemacyst are small flying Locust that "Kamikaze" into opponents. They are very dangerous, as shown in the cutscene between "Wrath" and "China Shop" in Act 1, where two Nemacyst spores take out a King Raven helicopter.
Fortunately, Nemacyst are very weak, and one shot from a Boltok Pistol is enough to kill one.
Not playable in multiplayer.
Seeders
Seeders are large creatures that sit in a huge Emergence Hole and produce Nemacyst to destroy COG soldiers.
Seeders are only vulnerable to the Hammer of Dawn.
Not playable in multiplayer.
Reavers
Reavers are airborne creatures that can be ridden by one or two Locust soldiers. The pilot can control a large chaingun mounted on the creature, while the other rider, either a Drone or a Theron Guard, fires a Hammerburst or Torque Bow from the back of the beast.
Reavers are easiest to kill with either a Chaingun turret, a Torque Bow or a Longshot.
Not playable in multiplayer.
Brumak
A Brumak is an enormous creature, more like a tank than anything else. It is heavily armed. Brumaks are never faced in Gears of War, so their weaknesses are unknown, but is most likely the Hammer of Dawn.
Not playable in multiplayer.
Gunners
These are Drones used to man Troika Turrets.
Not playable in multiplayer.
Locust Queen/Myrrah
This character is never seen, but is heard talking to the player at several points in the campaign, and to the Locust team in multiplayer.
Not playable in multiplayer.