Idris the Giant (Welsh: Idris Gawr; c. 560 – c. 632) was a king of Meirionnydd in early medieval Wales. He is also sometimes known by the patronymic Idris son of Gwyddno (Idris ap Gwyddno).
Cadair Idris, a Welsh mountain, literally means "Chair of Idris". Idris was said to have studied the stars from on top of it and it was later reputed to bestow either madness or poetic inspiration to whoever spent a night at its summit. According to John Rhys, there were three other giants in the Welsh tradition along with Idris – Ysgydion, Offrwm, and Ysbryn – and all of them have mountains named for them near Cadair Idris.