Reason

Reason is besides another minor differences, what makes humans human. A being is named human if is able to think, to use his reasoning. Reasoning is a kind of mind activity that consists in consciously represent the outter world, bringing sense and meaning in a coded language to interact with it.
It's a subjective activity done by a "ego", a differenciated being who (as a result of this activity) separates itself from the rest of the reality.
This capacity is only owned by mankind (in the degree and character that we understand the word "reason").
Thus we can create a artificial  being (man-made), a robot but only when it could reason it will be a human.