The bloated Overlord's fearsome demeanor serves as little protection for this slow, defenseless, and entirely vulnerable flying organism. Its primary function is to maintain the control link between the Zerg Overmind and its distant forces. In this respect, the Overlord is functionally equivalent to a Terran Supply Depot or a Protoss Pylon. Since each Overlord can only maintain control over a limited number of Zerg units, you must produce new Overlords regularly to support your ever-increasing military.

Once you upgrade your Hatchery to a Lair, three key evolutionary enhancement options become available that go a long way to increase the functionality of your Overlords. These include Pneumatized Carapace, which greatly increases your Overlords' speed and makes them much more useful for scouting purposes; Antennae, which increase your Overlords' field of vision and let them more easily detect incoming threats; and Ventral Sacs, which make Overlords functionally equivalent to cargo transports. The Ventral Sacs upgrade is only useful after Pneumatized Carapace, while Antennae, though convenient, is something of a luxury.

After evolving Ventral Sacs, an Overlord gains a storage capacity of eight slots. Drones, Zerglings, Broodlings, and Infested Terrans all use one slot, Hydralisks use two, Defilers use two, and Ultralisks use four. Since you'll have plenty of Overlords around, you can easily ferry great armies to remote distances.

Another valuable function of the Overlord is its innate ability to detect concealed enemies. Use it to spot invisible opponents like Terran Wraiths, Ghosts, Spider Mines, or even burrowed enemy Zerg. Always send a few Overlords into battle with your main force if you suspect retaliation from hidden enemies.

Since Overlords directly determine how many units you can support in battle, expect them to be targets of opportunity for your enemies. Defend your Overlords well; just throwing them all into a remote corner of the battlefield will not be enough, as a cunning enemy will find them and kill them off, thus crippling your army. Since Overlords are also useful for their transporting and scouting functions, expect to lose some over the course of a fight. Always make certain to have more than enough Overlords so their individual losses won't cripple your war effort.

Next: Zergling