Coleus was a Nomai geologist born outside the solar system, arriving via the Vessel and crashing on Ember Twin. He, along with his mentor Melorae, was instrumental in guiding the Nomai from Escape Pod 2 through a cave system to what became the site of the Sunless City.
While surveying caves on Ember Twin, he temporarily vanished by becoming quantum-entangled with a quantum shard, effectively teleporting himself to a cave with no other way in or out. His disappearance caused panic, but he ultimately found his way back unharmed and was praised for discovering that, if one can put themselves in the dark while in contact with a quantum object, one can become quantum with the object and effectively teleport to wherever the object is next observed.
Later in life, he took on an apprentice of his own, Cycad. The two participated in identifying a safe mining site (i.e. one that wouldn't disturb local fauna) on Timber Hearth during the construction of the Ash Twin Project.