The Ultramarines: A Legendary Chapter of Space Marines in Warhammer 40,000 The Ultramarines are a legendary chapter of Space Marines in the Warhammer 40,000 universe. They were founded by the Primarch Roboute Guilliman during the Great Crusade in the 30th Millennium, and have since become one of the most respected and powerful chapters in the galaxy. The Ultramarines are known…