It’s called Honour and Iron because of Ultramarines and Iron Warriors, get it?
Primarch Pilgrimage: Perturabo – The Hammer of Olympia by Guy Haley
Another book in which we learn Perturabo is just a bitter man-child.
Traitor Legions: Evil Wears a Civil Mask
Evil isn’t foaming at the mouth, it’s offering glory and rationalizations.