Mrlsst was the only planet in the sector with an indigenous alien race. It was a moist and humid world, with terrain dominated by marshes and sandy swamps. Nearly everywhere, one could find the towering cosmopolitan greenstalk plants that grew all over the planet, except the poles.
A thick asteroid field surrounded the planet, which was used for raw materials and was the location of several research stations.
Mrlsst was the home of the famous Mrlsst Trade and Science Academy, the best university in the sector, and one of the best beyond the Core Worlds.
The first contact between the Mrlssi and Humans occurred sometime before 7000 BBY. Mrlsst joined the Galactic Republic shortly thereafter. Canny Mandary Bertar represented the planet in the Galactic Senate, and after the Republic was reorganized into the first Galactic Empire, the Imperial Senate.
Thousands of years ago, the planet's continents were unstable, resulting in frequent groundquakes and tidal waves; the natives became used to losing possessions amidst such disasters, and came to appreciate knowledge as a result. The planet had grown much more stable by the time of the Galactic Civil War, but the tradition of learning endured among the Mrlssi.
Jedi Master Daakman Barrek hailed from Mrlsst.
Shortly after the Battle of Endor, the planet was the site of a battle between Rogue Squadron and Imperial Captain Loka Hask for the control of Phantom Project, a new cloaking device technology. Hask was eventually defeated, but the planet suffered heavy causalities.