He still retains his mind, even though he is in the grip of the Black Rage.
A Space Marine that lived more than a thousand years? This is a universe where everything is trying to kill you, and even with constant fighting he is still alive.
Being chosen as the overall commander of the Second Armaggedon War.
"For he today that sheds his blood with me shall be my battle-brother eternal."
Using the Spear of Telesto to banish Malfallax back to the Warp.
Using the Spear of Telesto to bring back the Blood Angels who had fallen to the Black Rage.
In Red Fury, his epic Last Stand against the Bloodfiend Alpha, his very back against the tomb of Sanguinius. What does our hero do when confronted by a mutant that had killed a Dreadnaught in melee? Gives a Badass Boast ("This is as far as you go"), stabs it in the heart with his combat knife, then grabs Mephiston's Force Sword to impale its secondary heart.