Overlords were evolved from the Gargantis proximae, a species of giant space-faring and semi-intelligent creatures which volunteered to be assimilated in order to avoid extinction. Once assimilated, they were used to help cerebrates control and coordinate their broods and scout using their enhanced senses.
The elongated appendages that hung from the underbellies of the Gargantis were evolved into an array of microscopic filaments that gather sensory and spatial information through intermittent pulses, which are then fed into the overlord's central nervous system. All data gathered is processed as fast as it is received, allowing overlords to navigate through any environment and relay tactical data to the Swarm.
Overlords possess a large, bulbous brain which is protected by a heavily armored weave of bone and cartilage. It is a large organ, with millions of nerves and synaptic contacts. The overlord's cerebral structure is complex with neural pathways woven throughout the body; but is heavily concentrated in its lower section and legs. It is through this system that overlords relay commands to the Swarm. The overlord's nerve system makes it a powerful psionic energy transmitter (its ability to broadcast psychic energy is unmatched) and to preserve this capability, the zerg only altered neurologically impotent parts from the Gargantis, including the carapace and pulmonary chambers. As a result, the overlord's core genetic matrix is atypically homogenous: over 90%. The minimal alterations also preserved memories; ancient overlords, essentially assimilated Gargantis, regained their individuality upon becoming feral. Dr. Talen Ayers proposed two theories as to why this was—one, the Gargantis had the properties the zerg desired, and as such, little modification of their genetic code was required. Two, the zerg are unwilling to meddle too deeply with the structural makeup of species that possess great psionic ability, knowing that even the slightest of changes can destroy this ability. He counted on the latter.
Unlike most other zerg breeds, overlords have a greater capacity to act on their own judgement, though their mental flexibility is still severely limited. Overlords typically only relay orders. They are technically capable of directly controlling lesser zerg, but only with extreme difficulty. After Kerrigan's defeat at Char, some overlords attempted to form pockets of organized zerg in the same manner as broodmothers. However, this was a token effort, and most zerg regressed to a feral state.
Overlords with the correct growth stimuli can carry other zerg within hollows in their hides. In this form they become deep-space transports; the importance of their function is underlined by the sheer number of overlords found accompanying zerg forces. As spacefaring creatures, an overlord's carapace pressurizes and seals whenever the creature flies through vacuum. Two species of unidentified symbiotic organisms seem to regulate these functions, though Dominion scientists have been unable to obtain any living samples—these organisms die within seconds if removed from their host overlord.
Overlords use helium-filled gas sacs and a weak telekinetic psi-ability for lift and motive power. This helium is generated through an efficient respiratory system distributed throughout the overlord's carapace. The excess helium is stored in thick sacs that contract and expand through rudimentary pulses, allowing overlords to regulate altitude and propulsion at will. They move quite slowly however.
By the Second Great War, overlords could disgorge creep to prepare the way for zerg conquests. This creep is produced by the overlord liquifying its internal organs, with the creep being stored in multiple glands near the overlord's head. The process is instantaneous and takes place when space is needed for transportation of zerg ground strains. Overlords can regrow their organs at will, and can modify them to derive substance from inhospitable environments. Also by the Second Great War, overlords could metamorphosize into overseers.
- For StarCraft gameplay information see: Overlord (StarCraft).
This article or section contains information about StarCraft: Ghost, which has been declared non-canon. Elements may be taken as 'flavor lore' however.
This following section contains information from concept art that may not be canonical.
- For StarCraft II gameplay information see: Overlord (StarCraft II).