Primarch

The Emperor made twenty of them in the late 30th Millennium, from a subset of his own DNA, and each one's genome became the template for one legion of Space Marines. They were meant to be generals: bigger, faster and cleverer than any human, and charismatic enough to hold an army together. Two of the twenty were later struck out of the Imperial records and have never been named, which is why the roster people can actually list runs to eighteen rather than twenty.