The Unicorn is a mystical creature with roots in Southeast Asian culture. A form of this beast was captured in ancient Indus Valley Civilization engraved seals, though it’s body was more reminiscant of a bovine, not an equine. Greek texts reference the Unicorn as a natural beast, which was thought to live in India. However, this thinking most likely stemmed from early accounts of rhinoceri.
In alchemical writings the Unicorn’s horn, known as an alicorn, is remarked to have special abilities. Such qualities include the curing of disease, the cleansing of water, and the detection of poison.
As an aside, it is important to note the differences between the Pegasus and the Unicorn. A Pegasus does not have a horn, and utilizes wings to fly, whilst the Unicorn has no such means for aeronautics.
The above image is from Edward Topsell’s “The History of Four-Footed Beasts and Serpents”.