In Scottish folklore the Ghillie Dhu or Gille Dubh (Scottish Gaelic pronunciation: [ˈkʲiʎə ˈt̪u]) was a solitary male fairy. He was kindly and reticent, yet sometimes wild in character. He had a gentle devotion to children. Dark-haired and clothed in leaves and moss, he lived in a birch wood within the Gairloch and Loch a Druing area of the north-west Highlands of Scotland. Ghillie Dhu is the eponym for the ghillie suit.

Ghillie is an English equivalent of the Scottish Gaelic word gille; Edward Dwelly, a Scottish lexicographer, lists gille as a "lad", "youth" or "boy" with dubh translating as "dark" or "dark-haired".

According to folklorist and scholar Katharine Briggs the Ghillie Dhu was a gentle and kind-hearted mountain spirit, or a "rather unusual nature fairy." The Ghillie Dhu was an individual male modern day fairy described by Osgood Mackenzie, a Scottish landowner and horticulturist, in his memoirs that were published in 1921. The fairy was generally timid, yet he could also be "wild".

Residing in the birch woods near Loch a Druing, in the north-west Highland area of Gairloch, he was mainly seen in the latter part of the 18th century. The woods are in a dip alongside a hilly area around 2 miles (3.2 kilometres) from where Rua Reidh Lighthouse was later built. One summer evening a local child named Jessie Macrae wandered into the woods and became lost. Jessie was found by the Ghillie Dhu who looked after her until the next morning when he took her home. Over a period of four decades the fairy was frequently seen by many people but Jessie was the only person he conversed with. Generally of a dishevelled appearance, he used green moss and leaves taken from trees as clothing. As implied by his name, he had black hair; he was of a small stature. His fondness of children is similar to that displayed by the little known Hyter sprite of English mythology.