Tetrarch

"‘Not true. Not if I have done what I set out to do. I didn’t raise the Legion solely to build an Imperium and fight a crusade. Crusades are finite. Wars end. I raised the Legion to have a successive function in peacetime too – as leaders, as statesmen, as rulers of the Imperium once it was built.’"

- Primarch Roboute Guilliman addressing tetrarch Valentus Dolor

"‘Space Marines excel at warfare because they were designed to excel at everything. Each of you will become a leader, a ruler, the master of your world and, because there is no more fighting to be done, you will bend your transhuman talents to governance and culture.’"

- Primarch Roboute Guilliman addressing Chapter Masters and Captains of the Ultramarines Legion

The Tetrarchs of Ultramar were a group of highly distinguished veterans of the Ultramarines Legiones Astartes. The 500 worlds, as the Realm of Ultramar was called, was divided up into four major fiefdoms under the dominion of Macragge. This was done by direct decree of Primarch Roboute Guilliman himself to improve the governance of his empire. Each of these domains was ruled from a major world by one of these 'Princes of Ultramar'. Every Tetrarch was a military governor and provided the Legion with a Champion and an Honour Guard. As each of them answered only to Lord Guilliman himself and controlled several worlds, his position was above that of any planetary governors or Chapter Masters of the Legion. The position could be compared to that of Sector Governs in the 41st millennium.

At the time of the Horus Heresy the Tetrarchs were: Preceding the Calth Atrocity, that world, given it's industry and shipards, it would have become a major world in it's own right. Chapter Master Aetheon of the 19th Chapter of the Ultramarines was rumoured to become the next Tetrarch. That name would possibly have to change though, as five major worlds would demand Quintarchs. However, the acts of the Word Bearers out an end to that dream.
 * Eikos Lamiad, Tetrarch of Konor
 * Tauro Nicodemus, Tetrarch of Saramanth
 * Stolos Amyntas, Tetrarch of Iax
 * Valentus Dolor. Tetrarch of Occluda