The creation of the Cybermen in the Doctor's universe occurred on the planet Mondas some time prior to the 20th century, probably in the distant past.

History

Cybermen of the Doctor's universe

One account states the planet Marinus was an earlier name for Mondas. According to this account, the Voord acquired Worldshaper technology to accelerate time and turn themselves into full cyborgs. The Cybermen would later remember this planet as Planet 14. (COMIC: The World Shapers)

Another account did not explain the earliest origins of the Cybermen, but showed Cybermen existed on Mondas alongside the Lizard Kings, the Mondasian versions of Silurians, as well as the Sea Devils. These Cybermen died out until centuries later when Mondasian archaeologists discovered the remnants of ancient Cybertechnology. Presumably, the Mondasians recreated the ancient Cybermen. (COMIC: The Cybermen)

Yet another account shows that as Mondas travelled beyond the outermost planets of the solar system, conditions on the planet deteriorated. The Fifth Doctor and Nyssa arrived on Mondas prior to the rise of the Cybermen. They discovered the survivors living in an underground city roughly on a parallel with Britain in the 1950s, although with more advanced technology. They witnessed the Mondasians slowly slide towards cyber-conversion, as the the Faction had. The Mondasian cyber-conversion program was conceived by the cybernetic gestalt intelligence controlling Mondas as a solution to the planet's increasingly desperate situation. (AUDIO: Spare Parts)

The Cybermen evolved and changed on Mondas. The CyberFaction, a group dedicated to more radical cyber-conversion, moved to Planet 14. The Mondans stayed on their home planet. (PROSE: Iceberg, REF:Doctor Who: Cybermen)

This obviously contradicts the explanation for "Planet 14" given previously.

Other universes

Independently, John Lumic, the CEO of Cybus Industries created the Cybermen of a parallel Earth. (TV: Rise of the Cybermen/The Age of Steel)

See Cybus Industries and John Lumic

Behind the scenes

Continuity contradictions

Taken at face value, the origins of the Cybermen given in the Doctor Who Magazine comics feature The Cybermen conflicts with that given in Spare Parts and neither accords very well with The World Shapers, which had earlier appeared in Doctor Who Magazine. Lance Parkin has speculated that perhaps Cybermen have originated in different planets and times independently, just as they had in different universes, as illustrated by the parallel universe Cybermen having no connection with the Cybermen of the main universe.

Alternatively, the Cybermen shown in The World Shapers may have preceded the ones in The Cybermen, though they do not match visually. (The former resemble the sleeker, later Cybermen while the Cybermen of The Cybermen resemble the ones of The Tenth Planet.) The explanation of the creation of Mondas by the Constructors of Destiny in The Quantum Archangel also contradicts that given in The World Shapers.

"Genesis of the Cybermen" storyline

Gerry Davis, who had co-created the Cybermen with Kit Pedler, had written "Genesis of the Cybermen", an outline for a Cybermen origin story which David Banks included in his Doctor Who: Cybermen.