Who are the Space Marines enemies?

The Top 9 Space Marine Killers

Exocrines.
Heldrakes.
Ravagers.
Daemon Princes with Malefic Talons.
Meganobz with Killsaws.
Triarch Praetorians.
Anyone and Anything Holding a Heavy Bolter.
Genestealer Cults Aberrants.

How long do Space Marines live?

The average age of a Space Marine who is dutiful to the Emperor and repelling enemies of the Empire is about 300-350 years. No Space Marine has ever been reported of dying of old age and all of them expect to die in battle against enemies of the Empire.

Why do Space Marines not wear helmets?

In order to make full use of their imporved senses ,Space Marines will remove their helmets. That is because the helmets interfere with sensation, especially sense of smell. Second reason: The helmet is damaged. Space Marine helmets are very complex technological devices, and can malfunction if hit.

Do Space Marines have commissars?

To assume that Space Marines have natural authority over Imperial Guard in all situations is ignorant. Also, the ranking structure of the Space Marines is different than the Guard. There are no corporals or privates or lieutenants or majors or colonels, ect. in the Astartes.

Can a guardsman become an inquisitor?

Yes, an Inquisitor can include pretty much anyone into his retinue. That is, you would have to be exceptional at your profession, be it a Guardsman, Arbitres, Navigator, Techpriest etc., to have an Inquisitor even consider taking you under their wing.

How do I become an inquisitor?

In order to become an inquisitor you would need to start off your career as an acolyte to an inquisitor filling in a specific role in that inquisitors retinue. After that if the inquisitor finds you to be worthy or an asset. They will recommend you to become an inquisitor.