u/Exist_Logic

The Excerpt in question :

>‘Despite our early issues and personal differences, Commander Branne, I would have no problem serving under you. Against overwhelming opposition, you rescued Lord Corax and the remains of your Legion from Isstvan. That is a feat worthy of respect and praise. You are a Hero of the Imperium, commander.’

>‘I am?’ laughed Branne. There were chuckles from the other legionaries, both Raven Guard and Imperial Fists. Since Isstvan, the commander had felt as if he had failed. The most important battle in the Legion’s history and he missed it. He and his warriors had been apart from the others, isolated from the bond that had brought the rest of the Legion together, Terrans and those of Deliverance. To hear Noriz speak of his actions in such terms allowed him for the first time to think differently about the matter. ‘If that makes me a Hero of the Imperium, we’ll have to come up with a new title for whoever kills Horus.’

>‘It’ll be Russ,’ said one of Branne’s honour guard. ‘Just you wait. Once the Space Wolves get involved, this’ll be over quick.’

>‘Maybe we’ll get to him first,’ said another.

>‘Sanguinius,’ said Noriz, silencing the debate. ‘The Sons of Fenris are far away, still likely dealing with the aftermath of Prospero. As much as I admire your enthusiasm, the Raven Guard cannot match the might of the Luna Wolves. No, when the Blood Angels hear of this treachery, there’ll be no stopping Sanguinius. Lord Dorn calls him the Angel of Death, and I can’t imagine Fulgrim, Perturabo, Lorgar or any of the others wanting to step between Horus and the Angel’s vengeance. It’ll be Sanguinius, mark my words.’

>Branne reached into his belt and pulled out a ring with two large keys on it. They were dull, much scratched and slightly bent, the wear of decades plain to see.

>‘I took these from the first man I killed during the liberation war,’ said Branne. ‘If Sanguinius kills Horus, they’re yours.’

>‘A wager?’ said Noriz.

>‘If you like,’ said Branne. ‘What do you offer up?’

>Noriz glanced at his legionaries and received nods of encouragement.

>‘All right,’ said Noriz. He unhooked a golden shield from the lanyard on his right shoulder plate and held it up to Branne. It was inscribed with a single word: ‘Narandia’. ‘My first battle honour, awarded for slaying an ork commander. If Russ gets to Horus first, you can have it.’

>This was greeted with claps and a cheer from the Raven Guard.

>‘I‘ll be watching your back, to make sure that you survive long enough to hand over that shiny medal,’ said Branne.

>‘And I will be watching yours, commander,’ replied Noriz, slapping his hand against Branne’s breastplate. ‘I have always desired to own a rusty set of keys.’

>Returning the keys to their pouch, Branne hoped that one of them would prove right. If Horus reached Terra, nothing would be certain.

My question is, what did Dorn see to have that high an opinion of Sanguinius