Before time, The Primordials battled with the Gods for dominion of Abier-Toril. The Primordials were (are) brutally powerful elementals forces at odds with the Gods. A Primordial named Dendar the Night Sepent stole the sun from the sky and plunged Abier-Toril into many days of darkness. Ubtao (known now as the Deciever) was a Primordial concerned with the land - and when he saw Dendar's desctruction of his realm, he sided with the Gods and lured Dendar into a great prison where he remains trapped to this day. At the end of the war, the Great AO divided the world into two; Abier would be home to the Primordials, and Toril would be ruled by Gods.
Ubtao stayed on Toril and was granted sole dominion of Chult where his Tabaxi people and Dinosaurs flourished. Ubtao roamed the land and guided his people through their Maze of Life. The Tabaxi people became one with the land and nurtured and protected Ubtao's realm. Ubtao built the great City of Mezro to become one of the greatest civilizations of its time. Ubtao appointed 7 Barae (Paladins) to rule over the City and be its protectors. Eventually, Ubtao tired of his disciples who had grown rich and greedy, and he left them to become one with the Jungle. The Chwingas are parts of Ubtao still as iare the rivers and the trees. Ubtao's spirit inhabits the Land and protects it agains t the return of Dendar.
Ras Nisi was amoung the most powerful and loyal of Ubtao's Barae. He had great dominion over life and death, and was able to raise great undead armies with a word. A race of people warred with the Tabaxi, and Ras Nisi - seeking to protect Ubtao's people, joined the conflict and waged a war of genocide against the invaders.
The Barae saw Ras Nisi's violence and condemned him. In response, Ras Nisi raised a great army of the Dead and laid Mezro to waste. To this day the remnants of Nisi's undead army still roams the land emblazoned with his symbol carved into their skin. Nisi himself disappeared but it is believed he lives deep within the Jungles of Chult even as his undead scour the land.