1986 Cyberman invasion of Earth

The Return of Mondas (AUDIO: The Ultimate Cybermen) was an attempted invasion of Earth by the Mondasian Cybermen. (TV: The Tenth Planet) Following the CyberFaction's invasion, this was the second Cyberman invasion of Earth recorded both in the history computer of the CyberFaction (PROSE: Iceberg) and in the Cyber-Documents of Earth, which were compiled into the CyberHive by the ArcHivist Hegelia. (AUDIO: The Early Cybermen)

Dating
Most accounts agreed that it occurred in December 1986. (TV: The Tenth Planet, PROSE: Iceberg, The Murder Game, Mondas Passing, AUDIO: The Reaping) However, others placed it in the 1990s (PROSE: The Power of the Daleks) or the year 2000. (PROSE: Doctor Who and the Tenth Planet, Doctor Who and the Tomb of the Cybermen)

Temporal status
This invasion of Earth was considered a temporal anomaly by the Time Lords, as it was not part of established Earth history as they understood it. Knowing that the First Doctor had been present on Earth during the invasion, some Time Lords suspected that the renegade Time Lord was directly responsible for this alteration to history, and the matter was raised at the Second Doctor's trial, being one of the gravest accusations of the case. However, the Doctor was able to successfully argue that he was not to blame. Later study by the Council for Temporal Research put these facts in relation with the mysterious temporal effects surrounding Mondas itself, and led to the speculation that an unknown time-active party, potentially a power-seeking renegade such as the Master, had systematically altered the Cybermen's timeline to allow them to grow into a large enough threat to endanger Gallifrey. (PROSE: The Cyber Files)

Before the invasion
"Aeons" prior to the invasion, Earth and Mondas were twin planets before Mondas drifted away to the edge of space. (TV: The Tenth Planet) Faced with a struggle to survive, the people of Mondas eventually developed into Cybermen, specifically becoming the CyberMondans, to try to survive. (AUDIO: Spare Parts)

According to some sources, a race of humanoids, all but identical to Earth humans, also resided on the planet Telos. Centuries prior to the 21st century, this race sought immortality and so perfected the art of cybernetics. As their bodies became old and diseased, they were replaced limb by limb with plastic and steel. Finally, the circulation and nervous systems were recreated, and their brains were replaced by computers, resulting in a separate breed of Cybermen known as the CyberTelosians. (PROSE: Doctor Who and the Cybermen) One account would claim that these Cybermen were forced to leave Telos and took refuge on Mondas, the long lost twin planet of Earth. (PROSE: Doctor Who and the Tenth Planet) As noted by the Twelfth Doctor, Mondas and Telos were both origin points for the Cybermen via parallel evolution. (TV: The Doctor Falls)

While travelling with Steven Taylor and Dodo Chaplet, the First Doctor met with Anu-Ak who'd shown him a recorded transmission of media coverage of the invasion before he'd experienced it. The Doctor determined to remember the details so as to impress his companions with his fore knowledge when it happened. (PROSE: The Golden Door)

Early incursions
Scout crafts from Mondas were sent to find Earth's location. The first expedition to find Earth crash-landed in the mountains of Austria around 1873, 113 years before their invasion. (TV: The Tenth Planet) However, due to the extensive damage sustained during the landing, they failed to report the location of Earth to Cyber-Control on Mondas, which was 200 light-years away. The Eighth Doctor made sure that all Cyber-Technology from the expedition was destroyed. (AUDIO: The Silver Turk)

The Seventh Doctor and Ace fought Cybermen in Nevada in 1954. These Cybermen were from Mondas, trying to invade. Their attack was delayed until 1986. (COMIC: The Good Soldier)

In 1970, the Cybermen attempted to disarm all of Earth's armies so that they could take over the planet without the death of a single Cyberman. Three Cybermen landed in the English countryside in a rocket and began tunnelling with a Cyber-Mole. With the Mole, they stole the doomsday bomb from Earth's underground secret weapons store and used it to put the entire Earth at ransom. The Second Doctor and John walked down the tunnel left by the Cyber-Mole and killed the Cybermen with ray guns before they could detonate the bomb. (COMIC: Cyber-Mole)

When Earth's most brilliant scientists gathered to witness the test flight of the Dart, Cybermen attempted to kidnap all of them to weaken Earth's military progress. The Second Doctor worked with the United States Air Force to destroy the Cyberman spaceships before the scientists could be taken. (COMIC: Test Flight)

Early scouts were encountered by the Time Lord Kelly and his companions eleven years prior to the main invasion. Additionally, according to the Cyber Files, pieced together from incomplete Matrix data by Jolennon and Palmac, (PROSE: The Cyber Files) the Cyberman invasion of Earth aided by Tobias Vaughn and foiled by the Second Doctor with the help of a newly-formed UNIT (PROSE: The Cyber Files, TV: The Invasion) actually predated the destruction of Mondas from the Cybermen's point of view, constituting an early incursion before Mondas had fully entered the solar system. (PROSE: The Cyber Files) However, according to other accounts, the Cybermen allied with Vaughn were either members of the CyberFaction, who had split off from Mondas much earlier and settled on Planet 14, (PROSE: Iceberg, AUDIO: The Early Cybermen) or else a force from the 30th century, far postdating the destruction of Mondas, who had been sent back in time after an encounter with the Seventh Doctor. (PROSE: Illegal Alien)

In 1984, two years before the return of Mondas, the Sixth Doctor left a damaged Cyber-Leader from the far future on Mondas, where it was considered faulty by its ancestors and taken to be reprocessed. (AUDIO: The Reaping)

Another Mondasian scout ship, crewed by Kreel and another found Earth only to be hit by a time storm. Kreel wound up buried in Edinburgh until the 2000s, surviving past Mondas' destruction, (AUDIO: Way of the Burryman) while his partner was displaced back to Berlin 1925. (AUDIO: Monsters in Metropolis) Both would be encountered by the Ninth Doctor, who would realise their connection after recalling one of the Cybermen warning him about the other. (AUDIO: The Forth Generation)

The invasion
Mondas eventually arrived in the Sol system in December 1986. The First Doctor met an advance force of CyberMondans near Snowcap Base in Antarctica, led by Cyber-Leader Regos Krang to prepare for Mondas's return and drain Earth's energy. Their takeover interfered with the Zeus IV rocket and resulted in the deaths of the astronauts onboard.

General Cutler planned to use the Z-Bomb but was prevented, and the Cyberman Gern took over International Space Command in Geneva, declared himself Cyber-Controller of Earth. Despite the Firt Doctor's warnings, Mondas absorbed too much energy and began to disintegrate, also killing the Cybermen on Earth who depended on Mondas for power. (TV: The Tenth Planet)

The Doctor
Shortly following the destruction of Mondas, the exhausted First Doctor began his regeneration. Though he was initially reluctant to change, he was convinced to do so following an encounter with the dying Twelfth Doctor who, unwilling to regenerate himself, was taken back to his own past by the TARDIS. (TV: The Tenth Planet, Twice Upon a Time) Incidentally, the Twelfth Doctor had also been forced to the brink of regeneration by a conflict with a separate branch of Mondasian Cybermen. (TV: World Enough and Time/The Doctor Falls) Ultimately, the two Doctors parted ways and regenerated into the Second and Thirteenth Doctors respectively. (TV: The Tenth Planet, Twice Upon a Time)

Ben and Polly
Twenty years after they helped the First Doctor prevent the return of Mondas in the then-future year of 1986 in their personal timelines, Ben Jackson and Polly Wright — who had gone their separate ways in life following a brief relationship after their return to Earth on 20 July 1966 — reunited on New Year's Eve in 1986, which was by then their present. (PROSE: Mondas Passing)

Earth
Professor Allison Williams led the scientific team which investigated the Cyberman ship in Antarctica. The Cyberships leftover from the invasion were examined and exploited by humans, allowing them to make advances in space travel, leading Sarah Jane Smith to describe the return of Mondas as "both the greatest disaster and most astonishing blessing ever to have happened to the human race." (PROSE: The Power of the Daleks)

Despite media coverage, (TV: The Tenth Planet) Ben believed that numerous governments had covered up the return of Mondas and the Cybermen invasion of the Snowcap. (PROSE: Mondas Passing) Indeed, by 2136, their involvement in the invasion was not known, with Terri Willis telling Ben that "it didn't make the newspapers". (PROSE: The Murder Game) However, the transmissions were still travelling in space thousands of years later, and Anu-Ak obtained one detailing the appearance of Mondas and the Doctor's involvement, including his picture. (PROSE: The Golden Door)

Around 2066-2068, the time of the Myloki war, the facts of the Cyberman invasion had been embellished by both the passage of time and official cover-up efforts. The invasion was instead remembered as a natural disaster. Mondas was remembered as “the Mondas Asteroid”, rather than a planet, which went supernova before hitting Earth's atmosphere. Alex Storm came across the original reports which revealed that Earth had in fact been visited, that Mondas was too big to be an asteroid, that its destruction had been deliberately triggered, and that an individual known as “the Doctor” was involved. The documents were shredded shortly afterwards to "save space". Nevertheless, by 2096, he still remembered the contents of the original documents and shared the details with Hal Bishop. (PROSE: The Indestructible Man)

The Cybermen
As late as 2070, Earth history books recorded that the Cybermen were all wiped out when Mondas was destroyed. However, there were groups of Cybermen that travelled into space prior to Mondas' destruction. The first settled on the planet Telos. (PROSE: Doctor Who and the Cybermen) The Sixth Doctor believed that the Cyberman colonisation of Telos was a consequence of the destruction of Mondas, (TV: Attack of the Cybermen) although another account suggested Telos and many other planets had already been colonised before the destruction of Mondas as a safeguard, (PROSE: The Cyber Files) and other accounts suggested the Telosian Cybermen were native to the planet rather than Mondasian colonists of any stripe. (PROSE: Doctor Who and the Tomb of the Cybermen, etc.)

These Telosian Cyberman returned to the solar system on 15 October 2070. Seeking the power used to destroy Mondas, the Cybermen infiltrated the human base on the Moon, when they intended to use to wipe out all life on Earth. They were opposed by the Second Doctor who accused the Cybermen of being motivated by revenge, while the Cybermen claimed that they were acting to eliminate dangers to the Cyberman Empire. Ultimately, their invasion attempt was thwarted by the Doctor. (PROSE: Doctor Who and the Cybermen, TV: The Moonbase)

According to the CyberHive history, compiled from the Cyber-Documents according to the judgement of ArcHivist Hegelia, the Cybermen did not infact seize Telos and subjugate the Cryons until after their attack on the Moonbase. Considered descendants of the early CyberFaction which left Mondas for Planet 14, these Cybermen were formally recognised as CyberTelosians by Hegelia. (AUDIO: The Cyber Nomads)

Another group of Cybermen who survived the destruction of Mondas settled on Lonsis, where they evolved into a form similar to that of the early CyberFaction and were unaware of the existence of Telos. The Shinx, a species whose planet was near to Lonsis, grew concerned about their presence, partly through the manipulations of the Celestial Intervention Agency, and eventually hired Hulbert Logistics to attack them. (AUDIO: Human Resources)

Centuries after the destruction of Mondas, the Neomorph Cybermen based on Telos used a alien time vessel to send a number of their own back to Earth in 1985, where they were to use the passing Halley's Comet to destroy the planet and thus prevent the destruction of Mondas the following year. This plot was ultimately foiled by the Sixth Doctor though, (TV: Attack of the Cybermen) as recorded in the CyberHive, a number of Neomorphs remained stranded in the 20th century, becoming the CyberIsomorphs. In 1988, these Cybermen attempted to transform Earth into their base planet, the New Mondas, but were destroyed by the Seventh Doctor. However, ArcHivist Hegelia proposed that these Cybermen, prior to their destruction, had supported and influenced the contemporary CyberFaction in Earth's solar system, setting them on their path to eventually become the Neomorphs, in an example of a bootstrap paradox. (AUDIO: The Ultimate Cybermen, TV: Silver Nemesis)

More advanced Cybermen from the future attempted again in 2005 to turn Earth into New Mondas as a way of "saving" humanity from itself, before the Eighth Doctor ustilised their section of the Time Vortex to destroy them. (COMIC: The Flood)

A New Mondas was eventually established but, along with Telos, was destroyed by 3985, (PROSE: Legacy, Theatre of War) at the hand of the Daleks, who detonated Oblivion Continuums they’d installed in newly converted Cybermen. (COMIC: Cyber Crisis)

Alternate timeline
In one alternate timeline in which World War III broke out in after the WOTAN crisis, the Cybermen landed in the Arctic unopposed and settled in the area. At one point, they negotiated a settlement with South Africa and its allies, providing them with weapons they could used to fight the United Kingdom. (PROSE: The Time Travellers) This timeline was later negated when the First Doctor defeated WOTAN in 1966, (TV: The War Machines) and encountered the Cybermen later in his travels. (TV: The Tenth Planet)