Editing Roboute Guilliman (section)

===Great Crusade and Horus Heresy===
Guilliman utilized his skills as a tactician and strategist to fight in his Father's crusade, preferring to form battle plans rather than actually participate in the fighting himself (though he still did his fair share of Xeno-killing). In the hopes of passing down some of his strategic expertise, he worked very hard to turn the Ultramarines into an army of thinkers. His primary rule as a commander was "Information is victory", emphasizing that Space Marines needed theoretical knowledge and practical experience, in other words, a sound understanding of the tactical situation and a means to achieve their objective. Given that battle plans proved to be the first casualty, Guilliman soon realised that he would need to refine his own strategies even as he codified them, lest they fall apart in the chaos of warfare. Additionally, where some legions developed rather useless hobbies like [[White Scars|calligraphy]] or [[Emperor's Children|sculpting]], Guilliman decided that all of his Astartes should be excellent civil administrators. This was because Guilliman knew that the Crusade would eventually come to an end, and suspected that [[World Eaters|a]] [[Death Guard|few]] [[Night Lords|legions]] would probably end up being dispensed with in one way or another. As such, he wanted to make sure his legion was not on the chopping block.

With over 250,000 legionaries, he managed to achieve compliance on the highest number of worlds during the [[Great Crusade]], but was surpassed in ''military'' victories by the [[Luna Wolves]], [[Space Wolves]] and [[Dark Angels]]. Meaning he was either a good diplomat or his crusade encountered more peaceful human societies. Guilliman also made a point to turn conquered planets into model military worlds, and the Ultramarines would not leave until a modern [[Planetary Defence Force]] was established. He really should've been put jointly in charge of administration post-Ullanor, which would've made premature, excessive taxation of newly integrated worlds a lot easier to avoid (and therefore fewer worlds would have joined Horus' rebellion). One counter-accusation by fan critics is that Guilliman didn't change a thing on Nuceria, a feudal world of people enjoying slaves and pit fights (not to say they were fucking responsible for the mess Angron turned into) on the inference that Nuceria was incorporated into his empire - however in Betrayer ch18, Nucerians was noted as isolated, and referred to Ultramar separately as "achingly close-by" forces contrasting their lip-service to being Imperials, which makes it unclear if they were incorporated into Ultramar. It may also have been that as a Legion Homeworld, Guilliman did not have the authority to do things. If he had, it would have been "going over Angron's head" and stepping on his turf. While it would have also made sense to have improved Nuceria, Guilliman may have left that for Angron to do himself. That sort of ineffective courtesy feels about right for Guilliman. Though it should be noted Angron never returned to his homeworld before destroying it and his legion recruited from other worlds.

[[File:Know No Fear huge.jpg|400px|thumb|right|''"Lorgar of Colchis. You may consider the following. One: I entirely withdraw my previous offer of solemn ceasefire. It is cancelled, and will not be made again, to you or to any other of your motherless bastards. Two: you are no longer any brother of mine. I will find you, I will kill you, and I will hurl your toxic corpse into hell’s mouth."'' - Roboute Guilliman, channeling Bryan Mills.]]
When civil war broke out, Guilliman was tricked by Horus into taking most of his Legion to Calth for a joint Ultramarines/[[Word Bearers]] engagement. While most of his Company Captains believed it was just the Warmaster flexing his muscles, Guilliman realised that there was a political angle to it as well: when the Emperor of Mankind rebuked [[Lorgar|Lorgar Aurelian]] for spreading the ''Lectitio Divinatatus'', he ordered the Ultramarines to burn Monarchia, capital city of Khur, as an example of what would happen to those who continued to defy the [[Imperial Truth]]. Guilliman carried out his orders and didn't show Lorgar any sympathy, but privately confided to some of his officers his discomfort in doing so, feeling that the total humiliation would irreparably damage relations between the XIII and XVII Legions. Guilliman saw this as a chance to mend fences and forge friendships the old fashioned way: by getting Space Marines to kill Orks side by side. Unfortunately, Horus and Lorgar used the Calth muster to kill nearly half the Legion in a surprise attack. When he found out Lorgar's treachery he personally declared to hunt Lorgar down and kill him, only to be attacked by some sort of [[Daemon]]ic proxy that blew up the main bridge of his flagship and voided him out. So Guilliman did what any other pissed off Primarch would do: go on a rampage against Word Bearers trying to board the ''Macragge's Honour'' by punching them to death. [[Wat|In near vacuum. Without a helmet.]] [[AWESOME|''For almost twelve hours.'']] ([[Dan Abnett]] is still pretty proud of that scene). Not long after that, [[Kor Phaeron]] tried to recruit him for [[Chaos]]' cause by stabbing him with a corrupted blade like Horus, but Guilliman wanted none of it and punched the Dark Cardinal off him so hard the old man had a heart attack. In the end, though, the Ultramarines managed to wrest control of their defense grid back and shoot any Word Bearer ship not retreating posthaste to smithereens.