The Space Marines or Adeptus Astartes are foremost amongst the defenders of Humanity, the greatest of the Emperor of Mankind’s warriors. They are barely Human at all, but superhuman; having been made superior in all respects to a normal man by a harsh regime of genetic modification, psycho-conditioning and rigorous training.
Space Marines are untouched by plague or any natural disease and can suffer wounds that would kill a lesser being several times over, and live to fight again. Clad in ancient power armour and wielding the most potent weapons known to man, the Space Marines are terrifying foes and their devotion to the Emperor and the Imperium of Man is unyielding. They are the God-Emperor’s Angels of Death, and they know no fear.
The Astartes are physically stronger, far more resilient and often mentally far removed from the lot of most normal Human beings. In the presence of the Astartes, most people feel a combination of awe and fear, and many cultures on the more primitive worlds simply worship them outright as demigods or angels of the God-Emperor made flesh.