The Welsh Dragon (Welsh: y Ddraig Goch, meaning 'the red dragon'; pronounced [ə ˈðraiɡ ˈɡoːχ]) is a heraldic symbol that represents Wales and appears on the national flag of Wales.

Ancient leaders of the Celtic Britons that are personified as dragons include Maelgwn Gwynedd, Mynyddog Mwynfawr and Urien Rheged. Later Welsh "dragons" include Owain Gwynedd, Llywelyn ap Gruffydd and Owain Glyndŵr.

The red dragon appears in the ancient Mabinogion story of Lludd and Llefelys where it is confined, battling with an invading white dragon, at Dinas Emrys. The story continues in the Historia Brittonum, written around AD 829, where Gwrtheyrn, King of the Britons is frustrated in attempts to build a fort at Dinas Emrys. He is told by a boy, Emrys, to dig up two dragons fighting beneath the castle. He discovers the white dragon representing the Anglo-Saxons, which is soon to be defeated by the red dragon of Wales.

The red dragon is now seen as symbolising Wales, present on the current national flag of Wales, which became an official flag in 1959.

The military use of the term "dragon" (in Latin, "draco") dates back to the Roman period and this in turn is likely inspired by the symbols of the Scythians, Indians, Persians, Dacians or Parthians. The term draco can refer to a dragon, serpent or snake and the term draconarius (also Latin) denotes "the bearer of the serpent standard". Franz Altheim suggests that the first appearance of the draco used by Romans coincides with Roman recruitment of nomad troops from south and central Asia during the time of Marcus Aurelius. One notable Draco symbol which may have influenced the Welsh dragon is that of the Sarmatians, who contributed to the cavalry units stationed in Ribchester from the 2nd to 4th centuries. Cohorts were represented by the draco military standard from the third century in the same way that the eagle Aquila standard represented the legions. The standard bearer of the cohort was called draconarius and carried a gilded staff with a dragon at the top. For instance, Gauls are attested to have marched under the dragon to distinguish the Gallic cohort from the Roman legions.

After the Roman withdrawal it has long been suggested that resistance to the Saxon incursion was led either by Romans or Romanised Britons, and this is evident in the names attributed in legend to those who led the opposition, including Ambrosius Aurelianus and perhaps Artorius. This could account for how the Roman terminology came to be adopted by Britons. From the first extant written records of the Britons, it became evident that dragons were already associated with military leaders. Gildas, writing in about 540, spoke of the Briton chieftain Maglocunus (Maelgwn Gwynedd in Welsh) as the "insularis draco".

The early Welsh or Brythonic poets, Taliesin and Aneirin both extensively use dragons as an image for military leaders, and for the Britons the word dragon began to take the form of a term for a war leader, prince or ruler. In Y Gododdin, Aneirin describes his patron, Mynyddog Mwynfawr as "the dragon" when he speaks of the "feast of the dragon". He also describes the war leader, Gwernabwy mab Gwen, as the dragon of the battle of Catraeth. Meanwhile, Taliesin, on Urien Rheged, described inexperienced and skilful leaders as dreic dylaw, 'inexperienced dragon' and dreic hylaw, 'skillful dragon' respectively. Owain ap Urien is called Owain ben draic, the chief dragon. Although not compiled until later, the main part of Y Gododdin and the heroic poems on Urien Rheged by Taliesin almost certainly date in origin to the sixth century.

The Welsh term draig, 'dragon' was used to refer to Welsh leaders including Owain Gwynedd, Llywelyn ap Gruffudd (Llywelyn the Last) and "the dragon" Owain Glyndŵr. Cynddelw Brydydd Mawr, a court poet to Owain Gwynedd, refers to him in one elegy, personifying him as "The golden dragon of Snowdonia of eagles".