“Brute force not work? It because you not use enough of it!”
–Karg, Ogryn Bone’ead.
Ogryns are huge, powerful abhumans fielded by the Astra Militarum as shock troops. Standing heads taller than an average man, these "savage, simple-minded" creatures are thick with bulk and muscle, and are descended from humans who were stranded on cold, high-gravity worlds in a time long forgotten. Their thick frames are capable of lifting immense weight and protecting them from most small weapons fire, and their great strength is invaluable for fighting on the front lines.
Once the Ogryns were rediscovered, the leadership of the Departmento Munitorum was able to find "appropriate uses for the big, dim abhumans". Carrying special, sturdily built, Ogryn-specific equipment like the brutal ripper gun and ripper saw, they are utilised as shock troops, deployed on the front lines to smash enemy units and cause as much damage and havoc as possible in as short a time as possible. While not as common as they once were, there are many regiments who still field Ogryns, either in dedicated Ogryn squads, or mixed in with other Guardsmen, who can help guide them and keep an eye on them, to "prevent them from hurting themselves and their comrades".
"Conveniently for the Imperial Guard", Ogryn are "incredibly loyal once befriended", and "will go to any ends to fulfil the commands of someone they trust". They worship the God-Emperor with a "child-like devotion", and are "more than happy" to charge into battle to keep the Imperium safe.