Tech-Priest

A Tech-Priest is an Adept of the Adeptus Mechanicus of the Imperium of Man who is generally responsible for maintaining all of the advanced technology of the Imperium, enlarging the Imperium's stocks of technical knowledge and conducting what little new scientific research occurs within the Imperium since the end of the Horus Heresy. They are the members of the Cult Mechanicus, the Cult of the Machine, a priesthood which forms an ecclesiastical hierarchy for the Cult Mechanicus of technicians, scientists, and religious leaders who believe that knowledge represents the only true divinity in the universe. The tech-priests provide the rest of the Imperium with its technicians, scientists and engineers. Though their bodies often incorporate many mechanical and electronic components as bionic replacements, tech-priests are fully human, unlike the cybernetic Servitors which carry out all the heavy and monotonous labor for them and the Imperium in general.

Fabricator-General
The Fabricator-General of Mars is the leader of the entire Adeptus Mechanicus, and as the Magos Mechanicus he is also the head of its religious counterpart, the Cult Mechanicus. He also invariably holds a position on the Senate Imperialis of the High Lords of Terra who collectively rule the Imperium since the Emperor's incarceration in the Golden Throne.

Magos
The Magi (sing. Magos) are the highest-ranking tech-priests in the Adeptus Mechanicus. They have demonstrated a complete mastery of a certain aspect of science or engineering, of which there are dozens. The rank of Magos accordingly consists of Magos Technicus, Magos Metallurgicus, Magos Alchemys, Magos Physic, Magos Biologis, Magos Genetor, Magos Cybernetica, etc.

Logis
A Logis is a logistician, analyst, and statistician. His purpose is to predict future trends and make forecasts about expenditure and needs. They are regarded as prophetic figures within the Cult Mechanicus.

Genetor
A Genetor is a high-ranking tech-priest specializing in the genetic sciences and biological engineering. Genetors are very common in the Adeptus Mechanicus, and often accompany Imperial forces on exploration missions to new worlds. They are also the members of the Adeptus Mechanicus responsible for testing the gene-seed of the Adeptus Astartes for purity and for creating new Space Marine Chapters.

Artisan
Artisans (also known as Constructors) design new machines, buildings, spacecraft, weapons, and other Imperial military hardware. They also control the vast labour forces of Servitors employed by the Adeptus Mechanicus.

Electro-priest
Electro-priests are fanatic warriors for the Cult Mechanicus, responsible for supporting other tech-priest warriors, combat Servitors and the Skitarri in battle. Their skins are engraved with a metallic electoo circuit which spirals around their bodies and interfaces with their minds, allowing them to build up a tremendous current of electrical energy. As Electro-priests enter battle they chant Cult of the Machine litanies, building up their electric energy and driving themselves into a frenzy of destruction.

Enginseer
Enginseers are engineer-mystics, possessing an unsurpassed knowledge of mechanical technology. Unlike most of the Priesthood of the Adeptus Mechanicus, Enginseers can be found serving in almost every Imperial institution (besides the Space Marines), and are often assigned to regiments of the Imperial Guard or other parts of the Adeptus Terra. Enginseers are highly-trained members of the Cult Mechanicus and are dedicated to the maintenance of Imperial technology. Through many years of study, they have gained the knowledge of the rituals and litanies that form the body of Imperial machine lore, as well as a deep understanding of the more practical disciplines of mechanics and electronics. In this role they serve across the galaxy, often in harm's way, as they will be called on to make repairs on the battlefield as well as in the workshop. They are a common sight on battlefields where the Imperial Guard has engaged large numbers of armoured vehicles, and are often accompanied by a retinue of Servitors for assistance or protection. Although most Imperial Guardsmen revere their vehicles enough not to risk annoying an Enginseer by "tinkering," the modification of vehicles to fulfill a certain need is inevitable, much to the chagrin of any Enginseers present. Enginseer contingents are also included in the mighty Titan Legions and the crews of the massive warships of the Imperial Navy, allowing them to perform emergency repairs in the heat of battle. Despite the respect they usually command among the units they are seconded to, Enginseers are not held in high regard among the Cult Mechanicus itself as their skills seldom contribute to the divine The Quest for Knowledge. As a result of their overwhelmingly practical knowledge, they are often viewed as lowly but necessary cogs in the workings of the Cult. Enginseers make use of bionic arm augmentations known as Mechadendrites that are connected to their central nervous system via the spine. They are used to help the Enginseer in repair operations, heavy lifting and for self-defence.

Rune-Priest
Rune-priests are responsible for performing the awakening rituals of machines by scribing runes and chanting Cult Mechanicus liturgies over them. They are versed in what the Mechanicus considers the most arcane branch of science: intuitive mechanics, speculation, and improvisation, and are famous for their lateral and often unorthodox thinking when strict logic and standard procedure fail.

Transmechanic
Transmechanics specialize in the use, repair and maintenance of communications technology. They are often assigned to other organizations of the Imperium.

Lexmechanic
A Lexmechanic's purpose is to compile and rationalize data so that it can be entered into a central computer (cogitator) repository. They work with computer-like speed and accuracy, assembling battle reports, economic statistics, planetary reports, etc. They are deployed throughout the divisions of the Adeptus Terra, but particularly in the bureaucracy of the Adeptus Administratum.'

=Sources=
 * Codex Imperialis, by Rick Priestley
 * Warhammer 40,000 4th Edition Rulebook, p. 121