It may have been invented by John Burness in his 1796 Thrummy Cap, A Legend of the Castle of Fiddes.
The poetic tale, Thrummy Cap, A Legend of the Castle of Fiddes (1796), written by John Burness (cousin of Robert Burns), was popular during the 19th century in the northeast of Scotland - it may be that Burness invented the legend.
[2] In the Methil tale, Thrummy Cap haunts a building at the harbor head - this was said to be the ghost of a wood merchant or carpenter, who was not paid for his work, and consequently drowned himself in Methil harbor, and took to haunting the building.
[4] In his 1848 Dictionary of Archaic & Provincial Words, James Halliwell-Philipps claimed the term was from Northumbrian fairy tales, and referred to a "queer-looking little auld man" with exploits taking place in vaults or cellars of old castles.
[5] "Thrummy Caps" also appear in Michael Aislabie Denham's 1850s list of spirits and fairies - in which Denham makes an unclear reference to the "Thrummy Hills" near Catterick, and also repeats the claim of it appearing in Northumbrian folktales.