Atropus

Atropus, known as the World Born Dead, was an undead primordial whose coming was a harbinger of death and destruction.

Description
Once a great power, little remained of Atropus but a decaying, disembodied head the size of a small moon, apparently made of black stone, heavily cratered, and covered with foul amniotic fluid. It was barren and rocky, roughly spherical and with mountainous ridges, deep trenches, and sharp spikes upthrusting from the ground. Noxious tar bubbled up from the craters. Glossy black stones, each 40 miles in diameter, formed its eyes. Atropals were said to be cast-off detritus from Atropus's substance. Undead conjured from nightmares also inhabited the world, and the master of them all was a headless, alien humanoid that was the focus of Atropus's incomprehensible intellect.

History
The sages who knew of Atropus all agreed that it was created when Ao created the first gods, though they didn't had a unified theory about how it was born. Some claimed Atropus was the rotting amniotic fluid of the first god of death, while others believed he was a divine mistake by Ao - the last god created, stillborn, immortal and dead upon creation. The truth, however, was that Atropus was really one of the Primordials.

Sages saw it for the first time in the ring of the planet Glyth. Atropus was attracted to the planet by the widespread death and destruction the mind flayers wrought on the other beings of their world. Atropus laid waste to the planet, leaving it dead and devastated.

Some of the few sages who knew about Atropus believed that its attention was turning toward Faerûn next, beginning its slow slide to the life-rich planet. They were ever vigilant for signs of its approach - a strengthening of necromancy and the spontaneous rise of the undead.