ERIS

                                      ERIS

Eris is the most massive dwarf planet in the Solar System, exceeding Pluto's mass by 28%. As such, it was a serious contender to be a tenth planet but failed to meet the criteria set out by the International Astronomical Union in 2006.

Eris was once considered for the position of tenth planet:

Eris is the most massive dwarf planet in the Solar System, exceeding Pluto’s mass by 28%. As such, it was a serious contender to be a tenth planet but failed to meet the criteria set out by the International Astronomical Union in 2006.

Eris was named after the Greek goddess of discord:

Fittingly, picking a name for the object took unusually long – more than 1.5 years after its discovery in 2005. Some of the rejected names were Xena, Lila, and Persephone (Pluto’s wife).

Eris may be the largest dwarf planet:

Eris is unquestionably the most massive of the known dwarf planets and was once thought to be the largest due to its relative brightness. After a stellar occultation in 2010 its diameter was calculated to be smaller than previously thought and more recent measurement suggested Pluto was larger than thought, however there is enough of a margin of error that either could be the largest.

All the objects in the Asteroid Belt could fit inside Eris:

Eris is still smaller than the Earth’s Moon, having about two thirds of the Moon’s diameter and one third of its volume.
Eris is a dwarf planet that lies at the outer reaches of our solar system. It was discovered in 2005 by professional astronomers who were examining images taken at California's Palomar Observatory two years previously.
As a dwarf planet, it fulfills most of the criteria for being a planet with the exception that it doesn't have the gravitational pull, because of its size, to clear space surrounding it of other celestial bodies.
It was previously known as UBU 313 and nicknamed Xena before it was given its current name. The International Astronomical Union (IAU) is responsible for naming and classifying planets.
Eris has a diameter of 2400km, which is slightly larger than Pluto's. In comparison, the Earth's diameter is 12,742km. Neither planets nor dwarf planets are perfect spheres, so this isn't the ideal way to measure their size but it is a reliable indicator.