K'Thoutek

K'Thoutek was a large comet (300 miles diameter) in Realmspace that circumnavigated the sun in an extremely elliptical orbit.

Inhabitants
Its only remaining inhabitant of a once large group of oortlings was their greatest wizard, turned into an undead haunt bent on revenge against the illithids who destroyed the colony. The appearance of the comet K'Thoutek was seen as a sign for the birth of a powerful person by astronomers on Toril.

Rumors & Legends
The appearance of K'Thoutek in the Torilian sky produced a variety of predictions by astrologers, usually associated with the coming of a powerful entity. If K'thoutek was seen in the vicinity of a nebula, the entity was said to be evil. The first sighting of comet was said to have predicted the birth of Elminster, while the following sighting several orbital periods later, when the comet was about to enter the Galleon Nebula, was said to have predicted the birth of the Simbul.

Inspiration
Similarly named comet Kohoutek travels around Earth's sun with a much longer orbital period.