20000 Varuna (provisional designation 2000 WR₁₀₆) is a large trans-Neptunian object in the Kuiper belt. It was discovered in November 2000 by American astronomer Robert McMillan during a Spacewatch survey at the Kitt Peak National Observatory. It is named after the Hindu deity Varuna, one of the oldest deities mentioned in the Vedic texts.

Varuna's light curve is compatible with the body being a Jacobi ellipsoid, suggesting that it has an elongated shape due to its rapid rotation. Varuna's surface is moderately red in color due to the presence of complex organic compounds on its surface. Water ice is also present on its surface, and is thought to have been exposed by past collisions which may have also caused Varuna's rapid rotation. Although no natural satellites have been found or directly imaged around Varuna, analysis of variations in its light curve in 2019 suggests the presence of a possible satellite orbiting closely around Varuna. Assumptions that the body is in hydrostatic equilibrium (and thus a dwarf planet) result in a calculated density too low for it to be a dwarf planet.

Varuna was discovered by American astronomer Robert McMillan using the Spacewatch 0.9-meter telescope during a routine survey on 28 November 2000. The Spacewatch survey was conducted by McMillan at the Kitt Peak National Observatory near Tucson, Arizona. At the time of discovery, Varuna was located at a moderately dense star field close to the northern galactic equator. Although Varuna was not detected by McMillan's real-time computer software, he was able to identify Varuna moving slowly among the background stars by manually comparing multiple scans of the same region using the blinking technique. After McMillan's observing shift, follow-up observations of Varuna were conducted by astronomer Jeffrey Larsen in order to confirm the object. By the end of Larsen's observing shift, both McMillan and Larsen had made a total of 12 observations that spanned three nights.

The discovery of Varuna was formally announced in a Minor Planet Electronic Circular on 1 December 2000. It was given the provisional designation 2000 WR₁₀₆, indicating that it was discovered during the second half of November 2000. Varuna was the 2667th object observed in the latter half of November, as indicated by the last letter and numbers in its provisional designation. At the time, Varuna was thought to be one of the largest and brightest minor planets in the Solar System due to its relatively high apparent magnitude of 20 for a distant object, which implied that it might be around one-fourth the size of Pluto and comparable in size to the dwarf planet Ceres.

Subsequently, after the announcement of Varuna's discovery, precovery images of Varuna were found by German astronomers Andre Knofel and Reiner Stoss at the Palomar Observatory. One particular precovery image, which was taken with the Palomar Observatory's Big Schmidt telescope in 1955, showed that Varuna was located three degrees away from its extrapolated location based on the approximate circular orbit determined in December 2000. The oldest known precovery image of Varuna was taken on 24 November 1954. These precovery images along with additional observations from Japan, Hawaii, and Arizona helped astronomers refine its orbit and determine Varuna's proper classification.

In January 2001, Varuna was assigned the minor planet number 20000 by the Minor Planet Center as its orbit was well determined from precovery images and subsequent observations. The minor planet number 20000 was particularly chosen to commemorate Varuna's large size, being the largest classical Kuiper belt object known at that time and was believed to be as large as Ceres. The number 20000 was also chosen to commemorate the coincidental 200th anniversary of the discovery of Ceres, which occurred in the same month as the numbering of Varuna.

Varuna is named after the eponymous Hindu deity Varuna, following the International Astronomical Union naming convention for non-resonant Kuiper belt objects after creator deities. The name was proposed by Indian choreographer Mrinalini Sarabhai, and was approved by the IAU in March 2001. Varuna is one of the oldest Vedic deities of Hindu literature, being mentioned in the earliest hymns of the Rigveda. In Hindu literature, Varuna created and presided over the waters of the heaven and of the ocean. Varuna is the king of gods and men and the universe, and has unlimited knowledge.

Planetary symbols are no longer much used in astronomy, so Varuna never received a symbol in the astronomical literature. There is no standard symbol for Varuna used by astrologers either. Denis Moskowitz, a software engineer in Massachusetts who designed the symbols for most of the dwarf planets, proposed a symbol for Varuna (): it derives from the Devanagari letter va व and Varuna's snake-lasso. This symbol is occasionally mentioned on astrology websites, but is not broadly used. Another sometimes seen is a variant of Neptune ( with a globe and outward-facing tines), as Varuna is the Hindu equivalent of Neptune.