Halvlad

Halvlad was an ancient Mondasian dictator, ruling the planet Mondas after it drifted away from the solar system but before the full conversion of the population into the first Cybermen — dated to 71567 years before the 1986 Cyberman invasion of Earth by the Cyber Files.

Halvlad was a mysterious figure to the Time Lords due to the peculiar temporal field surrounding Mondas which usually made direct observation of its past impossible. Only a brief three-week period of Halvlad's reign could be observed before the field clouded up again. During this time, the Time Lords were able to observe that Halvlad was ruling the whole of Mondas with the help of "early Cybermen". He led these forces through a war with the planet Fareah, located on "the outer arm of the Galaxy". (PROSE: The Cyber Files)

Behind the scenes
More thorough information about Halvlad was given in the Cyberman history contained in the reference book The Cybermen, which is not a valid source for this Wiki. It made it clearer that Halvlad was conceived as a "creator of the Cybermen" figure, equivalent to Davros for the Daleks.

As related there, Halvlad was a "ruthless though brilliant" cybernetic engineer. A precocious genius, he spent his childhood as a loner, and lost his parents to a tunnel collapse at an early age. He became Director of Research of the Secondary Academy of Mondas at an early age, and garnered acclaim for a "technological breakthrough" which improved the "geoformic generators" that provided Mondas with its power. However, he came to believe that "because technology had been sacred to the Mondasians since the time of Xtiloth, the ultimate destiny of the race was to fuse with technology" and rule the galaxy. The war between Mondas and the Fareans began during his lifetime, and saw the first use of a battalion of volunteer "Cyborgs", whose bodies were augmented with cybernetics without their brains being altered. Enraged when parties like the Forma Mathematica vetoed him taking his experiments further, he fomented a military coup and created hundreds more Cyborgs with more refined mechanics. After crushing a Mondasian rebellion led by the Forma Mathematica's supporters, he made short work of the Fareans with his new Cyborgs.

Afterwards, Halvlad stayed in power and continued to pursue improvements for the Cyborgs, intending to use them as a secret police to support his dictatorship and, ultimately, as invasion forces so that when Mondas next drifted towards an inhabited planet, Mondas would invade first rather than be attacked. Running out of volunteers, he began forcibly converting dissidents and criminals. Eventually, "he replaced the Cyborgs' organic brains with sophisticated computers to create the ultimate battle machine — the Cybermen". However, the newly-minted Cybermen, who were absolutely logical with the survival of the Mondasians as their sole purpose, quickly deposed Halvlad and converted him into an ordinary Cyberman, as they thought his unchecked lust for power and conflict was itself a threat to the long-term survival of Mondas.