Cybermen: 

Millennia ago, during prehistoric times, the planet Mondas, sister planet to the Earth, was knocked out of solar orbit and drifted into deep space. The Mondasians, already far in advance of Earth's technology and fearful for their race's survival, sent out spacecraft to colonise other worlds, including Telos, where they pushed the native Cryons aside and used the planet to house vast tombs where they could take refuge in suspended animation when necessary. 

On Mondas, the Mondasians were dying out. I in order to survive and continue the race, they replaced most of their bodies with cybernetic parts. Having eventually removed all emotion from their brains, to maintain their sanity, the natives installed a drive propulsion system so they could pilot the planet itself through space. As the original race was limited in numbers and were continually being depleted, the Mondasians — now Cybermen — became a race of conquerors who reproduced by taking other organic beings and forcibly changing them into Cybermen. The move to "cybernise" Mondasians must have commenced on Mondas before they conquered Telos. Otherwise, there must have been some ongoing contact between Mondas and Telos after it was conquered, or the move to develop into Cybermen must have been paralleled after that point.

The Cybermen are humanoid, but have been cybernetically augmented to the point where they have few remaining organic parts. In their first encounter with the Doctor, the First Doctor, the only portions of their bodies that still seemed human were their hands. By their next encounter, with the Second Doctor on Earth's moon, their bodies were entirely covered up in their metallic suits and their hands had been replaced by two finger claws. By their the time of their encounter with the Fourth Doctor on Space Station Nerva, their hands were changed back to having five fingers.

As they are relatively few in number, the Cybermen tend to use covert activity. They scheme from hiding and often use human pawns or robots to act in their place until they have to appear. They also seek to increase their numbers by converting others into Cybermen (a process known as "cyber-conversion"). It is presumed, and often implied, that beneath their suits still exist organic components and that they are not true robots. During their encounter with the First Doctor, a Cyberman tells a group of humans that "our brains are just like yours". However, by the time they encounter the Sixth Doctor,  this seemed to have been entirely replaced with electronics. In their confrontation with the Second Doctor on the planet Telos, veins could be seen through the domed head of the Cyberman Controller. Similarly, the Cyber-Controller encountered on a parallel Earth by the Tenth Doctor, has a brain that is visible through the dome. These Cybermen are usually constructed from human brains bonded to a Cyberman exoskeletal shell with an artificially grown nervous system threaded throughout, although direct grafting of cyber-components is another method of conversion. When they encountered the Fifth Doctor, human chins were vaguely visible through a clear perspex area on the helmet to suggest some kind of organic matter. However, during the encounter at Nerva Station, the Fourth Doctor states that they are "total machine creatures".

Although the Cybermen often claim that they have done away with human emotion, they have exhibited emotions ranging from anger to smug satisfaction in their confrontations with the Doctor. The Cyber-Leader, who is leading the invasion of this Earth from the parallel Earth, expresses clear frustration at the humans' refusing to surrender, although he later criticizes the Tenth Doctor for showing emotion. There are also Cybermen who, on occassion, retain memories of their lives before they were converted. These memories have caused varying emotional responses among this group. On the parallel Earth, a converted Jackie Tyler recognizes Peter Tyler as he and Rose Tyler (from this Earth) attempt to sneak into a conversion plant to try and save her. Her only response is to say she recognizes him and then to try and capture him. The Tenth Doctor is able to defeat the Cybermen on the parellel Earth by shutting down their emotional inhibitors, enabling them to "see" what had become of them. The realization of what they had happened led them to either simply shut down out of sheer horror, or partially explode. When the parallel Earth Cybermen invade this Earth, appearing initially as "ghosts", several members of Torchwood recieve various levels of conversion. Initially, three members receive ear-bud implants that allow the Cybermen to control their activities. They are used covertly to open the rift to allow the reamining Cybermen to come through. Once discovered, the ear-bud was removed and it was discovered that it connected straight to their brain via strands of what appeared to be nervous tissue. Yvonne Hartman is able to retain at least some elements of her personality in order to prevent the advance of a group of other Cybermen, and is last seen weeping what appears to be either an oil-like substance or blood. A partial conversion led to a degree of insanity in Lisa Hallett, which was retained even after she transferred her brain into a human body.  

Cybermen have a number of major weaknesses, of which the most notable is the element gold. Initially, it was explained that, due to its non-corrodible nature, gold essentially chokes their respiratory systems. For example, the glittergun, a weapon used during the Cyber-Wars in the future, fired gold dust at its targets. However, in later Cybermen, gold appeared to affect them rather like silver affects werewolves, with gold coins or gold-tipped bullets fired at them having the same effect. Gold, however, is not known as a weakness to early or more recent Cybermen. Other weaknesses of some Cybermen appear to be solvents, gravity based technology, excessive levels of radiation, and  are also rather efficiently killed when shot with their own guns. On the parallel Earth, an EMP(Electro-Magnetic Pulse) grenade is shown to disable a Cyberman and shut down its emotional inhibitor. 

Some Cybermen are given titles such as "Cyber Leader" (or variants thereof), "Cyber Lieutenant", "Cyber Scout" or the "Cyber Controller". The Cyber Controller in particular has appeared in multiple forms, both humanoid and as an immobile computer Reference has also been made to a "Cyber Planner" or "Cyber Director", although these may not be the same being as eachother or as the "Cyber Controller". The Controller seen (and destroyed) in various serials also may or may not be the same consciousness in different bodies. It appears to recognize and remember the Doctor from previous encounters.  

The Cyber-Controller on the parallel used the brain of John Lumic, the creator of the Cybermen on that world. He is later destroyed. When the parallel Earth Cybermen invade this Earth, a new Cyber-Leader appears. He is also destroyed. When this occurs, mention is made of downloading his data files into another Cyberman unit, which is then upgraded to Cyber-Leader.

Weapons:

Over the years Cybermen have been shown with various forms of weaponry. When originally encountered by the First Doctor they had large energy weapons that attached to their chests. When meeting the Second Doctor on the moon, the Cybermen had two types of weaponry: an electrical discharge from their hands, which stunned the target, and a type of gun. They also made use of a large laser cannon with which they attempted to attack the base itself. Facing the Seond Doctor again, this time on the planet Telos, the hand discharge weapon was again present. They also used a smaller, hand-held cyber-weapon shaped like a pistol that was described as an X-ray laser. In a third encounter with the Second Doctor on human space station, the Cybermen had "death rays" built into their chest units as well as being able to use the discharge from their hands to operate machinery. In a fourth confrontation with the Second Doctor, during an attempted invasion of Earth, the Cybermen carried large rifles for medium distance combat as well as having the same chest units. During an encounter with the Fourth Doctor on Nerva station, the Cybermen's weapons were built into their helmets. They may also have carried powerful hand weapons. In subsequent encounters with the Doctor, the Cybermen are seen to be armed almost exclusively with hand-held cyberguns.

The Cybermen have access to weapons of mass destruction known as cobalt bombs or Cyber-bombs, which the Fourth Doctor states were banned by the galactic Armageddon Convention.A "Cyber-megatron bomb" was mentioned during an attempted invasion of Earth in which they were stopped by the Second Doctor. This bomb was supposedly powerful enough to destroy all life on Earth. In a encounter with the Fifth Doctor, the Cybermen also used androids as part of their plans to invade Earth.

During their first encounter with the Tenth Doctor, the parallel Earth Cybermen electrocuted their victims by touching them and at first carried no other weaponry. During their attempted invasion of this Earth, the parallel Earth Cybermen are equipped with retractable energy weapons housed within their forearms, but also use modified human weapons to battle the Daleks. The partially converted Lisa Hallett used her electrical touch against the Torchwood team, as well as an energy beam fired from her arm which could only stun the part of the body it was aimed at.

The Cybermen also use smaller, cybernetic creatures called "cybermats" as weapons of attack. They are first used aginst the Second Doctor and the human archaeological expedition on the planet Telos. Here, they resembled oversized metallic silverfish and had segmented bodies with hair-like tactile sensor probes along the base of their heads, which were topped with crystalline eyes. The Second Doctor described them as a "form of metallic life," implying that they may be semi-organic like the Cybermen, and that they attacked by feeding off brain waves. A second type of cybermat, seen in the conflict with the Second Doctor on the human space station, was used for sabotage and was able to tune in on human brainwaves. They were carried to the "Wheel" in small but high-density sacs that sank through the hull of the space station, causing drops in air pressure. These cybermats had solid photoreceptors for eyes instead of crystals. The Second Doctor used an audio frequency to jam them, causing them to spin, crash and disintegrate.

The third model, seen on Nerva Station in a conflict with the Fourth Doctor, was a much larger, snake-like cybermat that could be remotely controlled and could inject poison into its victims. It had no visible eyes or other features, and was as vulnerable to gold dust as the Cybermen were.

The Earth Invasions:

•  Circa 1970:  A group of Cybermen from "Planet 14" ally themselves with industrialist Tobias Vaughn, who installs mind control circuits in electrical appliances manufactured by his International Electromatics company, paving the way for a ground invasion. This is uncovered by the newly formed United Nations Intelligence Taskforce(U.N.I.T.), who repel the invasion with the help of the Second Doctor.
• 1986: The First Doctor meets an advance force of Cybermen that land near an Antarctic space tracking station. This advance force was to prepare for the return of Mondas to the solar system. As Mondas approaches, it begins to drain Earth's energy for the Cybermen's use, but in the process absorbs too much energy and disintegrates. The Cybermen on Earth also fall apart as their homeworld is destroyed.
• 1988: A fleet of Cyber warships assembles to convert Earth into a New Mondas. A scouting party is sent to Earth in search of the legendary Nemesis statue, a Time Lord artifact of immense power made of the "living metal" validium. Due to the machinations of the Seventh Doctor, however, the Nemesis destroyed the entire Cyber-fleet instead.
• 2007: Five million Cybermen from a parallel Earth stream through a breach between universes to invade Earth and must instead fight a war with the Daleks. They were eventually pulled back into the Void by the actions of the Tenth Doctor.
• 2012: The inert head of a Cyberman is part of the Vault, a collection of alien artifacts belonging to American billionaire Henry van Statten. Acccording to its label, it was recovered from the London sewers in 1975 and presumably came from the 1970 invasion attempt.
• Mid-21st century: Mankind has reached beyond its planet and set up space stations in deep space. One of these, Space Station W3, known as "The Wheel," is the site of a takeover by Cybermen who want to use it as a staging point for yet another invasion of Earth. The Second Doctor and his companions prevent this. 
• 2070: Earth's weather is being controlled by the Gravitron installation on the Moon. The Cybermen plan to use the Gravitron to disrupt the planet's weather patterns and destroy all life on it, eliminating a threat to their survival. This attempt is also stopped by the Second Doctor.

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