Cybermen are the steel-clad soldiers of total logic and utterly cold reasoning. They have no emotions or personality, they function solely on intelligence and sense.
They were once humans from the planet Mondas, whose bodies were failing piece by piece, forcing cybernetic augmentations as the only option for those who wished to survive. But as their bodies continued to fail, the inhabitents of Mondas developed a full-body prosthesis to house the brain inside, and thus the Cybermen were born.
Cybermen are giants, reaching around 7 feet in height, clad entirely in silver body-armour, and are easily recognisable from the twin handles that frame their heads.