The Marines Errant are a Loyalist, fleet-based Space Marine Chapter credited in the Mythos Angelica Mortis as successors of the Eagle Warriors Chapter, giving them Ultramarines lineage. They were created late during the 23rd Founding in the 37th Millennium, to repair the gap left in Imperial military forces by the loss of other Chapters. The Chapter was well-named, for over the millennia since their Founding, the Chapter's Battle-Brothers have been active throughout the entirety of the Imperium and often far beyond its borders. The Chapter has shown a tremendous resilience and flexibility that have allowed it to participate in a broad range of Imperial Crusades even while its Battle-Brothers fervently venerate the dictates of the Codex Astartes.