Gretharans were a protohumanoid race which had once settled the planet Icaria Prime. They were distinguished by long, muscular necks, large skulls, long, slender limbs, and a compact, muscular torso.

Little was known of the Gretharans, as they were wiped out in a war with the Letheans in the mid to late 21st century. They did leave a significant quantity of writings behind, in a language known as High Gretharan. Many of these writings heavily referenced a weapon called the Krialta, a legendary object which they believed would drive away their Lethean enemies. The Gretharans were also believed to have been of a relatively low technological level, though talented artisans.

In the 2370s, an archaeological team from Cambridge University succeeded in discovering the Krialta on Icaria Prime, inadvertantly activating it and causing psychological distress to the majority of the dig team, and others at the site. The site also uncovered some of the oldest Gretharan artifacts ever, potentially pushing the date of their initial settlement of Icaria Prime to the early 20th century. (CoE eBooks: Remembrance of Things Past, Book I, Remembrance of Things Past, Book II)