Cyberman

Cybermen are a type of cybernetically augmented humanoids. They have varied greatly in design, with different offshoots factions throughout time and space. However, the two major groups, from which all other known versions are derived, are the Mondasian Cybermen, which originated on the planet Mondas, Earth's twin planet in the Doctor's universe, and the Cybus Cybermen, which originated on Earth in an alternate universe.

Despite the different origin and other differences, there is a number of similarities between both groups of Cybermen. For the most part, they have both lacked individuality or names. Cybermen no longer possessed emotions and viewed them as a weakness. They have frequently attempted to physically and mentally re-engineer humans and other humanoids into Cybermen, via a process called "cyber-conversion" or "upgrade"

Mondasian Cybermen
These Cybermen were originally a wholly organic species of Near-Humans who originated on Earth's former twin planet, Mondas. Mondas drifted into the outer solar system and to survive, the natives of that world adapted by turning themselves into cyborgs. (DW: The Tenth Planet) Eventually, all of the Mondasians underwent forced cyber-conversion. (BFA: Spare Parts). Many of them left Mondas and eventually developed into separate groups without connection with one another.

Nearly all were silver in colour, with the exception of a a black variety which also existed in the London sewers (DW: Attack of the Cybermen). They also exhibited exposed circuitry and tubing which may contain hydraulic fluids for motion, covering a rubber or mylar-like outer skin. The CyberMondasians which the Doctor met on Snowcap Base in 1986 had undergone a less radical conversion and still retained biological hands; it is possible these Cybermen were prototypes. (DW: The Tenth Planet) All other Cybermen were entirely covered up in their metallic suits. (DW: The Moonbase onwards)

These Cybermen had a number of major weaknesses, of which the most notable was the element gold. Gold, having a non-corrosive nature, choked their respiratory systems. (DW: Revenge of the Cybermen). 20th century guns barely phased Cybermen, though explosives and bazooka shells were capable of taking them down. (DW: The Invasion, Silver Nemesis) UNIT would develop gold-tipped rounds for Cybermen. (DW: Battlefield) In later centuries, the Cybermen would take hits from laser guns and energy weapons: at close range, this could destroy them. (DW: Earthshock)

Cybus Cybermen
This type of Cyberman originated in another universe, where they were created by John Lumic, the owner of Cybus Industries. His Cybermen believed that all people must be "upgraded" to Cyber-form so that information is never lost and that the Humans physical and emotional weaknesses are abolished.

Cyber-conversion usually involved painfully removing the brain of the subject and placing it within a suit of armour. Once complete, the newly developed Cyberman had a special implant placed within them, which prevented them from feeling their emotions. However, if the implants were disrupted, then the Cybermen entered into a traumatic state as they were overloaded by the pain of the conversion, resulting in them dying in agony or their heads exploding from the overload of emotions. (DW: Rise of the Cybermen / The Age of Steel).

The Cyber-suit was constructed from bulletproof steel. These exo-structures were stauncher and more heavily built than the Cybermen of Mondas. A chest plate with the Cybus Industries logo housed a "heart of steel", the function of which is unclear, and the emotional inhibitor chip. The brain was contained within the head. Artificially grown nervous tissue was threaded throughout the body so the Cyberman responded like a fully biological organism. (DW: The Age of Steel) Without a brain inserted, the Cyber-suit was a robot which apparently had sufficient processing capacity to pursue and attack a human target, even it's head alone. (DW: The Age of Steel, The Pandorica Opens) The weakness for gold was not present in these alternate Cybermen.

Unification?
While no contact between the two major groups of Cybermen has been documented yet, there exist some Cybermen that share characteristics of both, which indicates that such contact could have taken place. While they greatly resemble the Cybus Cybermen and are said to be brains in metal shells like the Cybus creations, their use of Cybermats and their awareness of the fact that the Doctor is a Time Lord, and his reference to "races" conquered by them further indicate Mondasian origin.

An army of such Cybermen was buried under the ice in the Arctic Circle for tens of thousands of years after being hit by a temporal storm. An excavation began to awaken the army, releasing Cybermats which in turn created Cyberslaves. The Doctor arrived on May 4th 2010 and stopped their awakening. He blew up their base and put them back into stasis. (VG: Blood of the Cybermen)