Dreadnought

A Dreadnought is a Space Marine who has proven himself invaluable to the Imperium. Therefore, He is implanted into a hulking robotic armoursuit at the moment he is mortally wounded, usually only if he is dismembered, or his implants cannot handle the sheer bulk of his wounds. It is one of the greatest hounors any Space Marine can have bestowed onto him. However, the Grey Knights chapter sees this as a dishounnor, their final resing place is to be a Masoleum on Holy Terra set aside just for the Grey Knights. This is not to say that there are no Grey Knights Dreadnoughts, just that they are few and far inbetween.

Chaos
Chaos dreadnoughts are feared, not revered, and rightly so, as they are quite mad. They are tied down during transit.