红龙（Y Ddraig Goch）最早是由塞尔特人所信奉的象征，后来和英雄亚瑟王传说所结合。

路特王统治时期，每年五月都有可怕的叫声，引发很多灾难。路特王求助于兄弟李瓦，李瓦告诉他是两条一红一白的龙打斗所造成，叫声就源自红龙的痛苦悲鸣。路特王受李瓦的建议下，在不列颠中心挖了深坑并灌入蜂蜜，到晚上两条龙打累后到坑里喝蜂蜜，路特趁龙睡觉时用布料包住牠们并放入石棺，埋在史诺多尼亚的Dinas Emrys。

伏提庚王（Vortigern，曾为罗马边境辅军，西元409年罗马自列颠撤兵后崛起的塞尔特人王）因撒克逊人违约起兵而退守威尔斯，想要在Dinas Emrys创建城堡，但每天半夜建城的原料都会消失。不久国王听巫师建议找来了当时才七岁的梅林，梅林并告诉国王两条龙的事。国王挖开地面发现那两条龙，龙醒来后又大打出手，最后红龙击败并赶跑了白龙。梅林表示白龙代表撒克逊，而红龙代表国王的子民，并告诉国王的子民必将击退撒克逊人。

The Welsh Dragon – Welsh:Y Ddraig Goch ("the red dragon") pronounced [ə ˈðraiɡ ˈɡoːχ] – appears on the national flag of Wales. The oldest recorded use of the dragon to symbolise Wales is in the Historia Brittonum, written around AD 829, but it is popularly supposed to have been the battle standard of King Arthur and other ancient Celtic leaders. Its association with these leaders along with other evidence from archaeology, literature, and documentary history led many to suppose that it evolved from an earlier Romano-British national symbol. During the reigns of the Tudor monarchs, the red dragon was used as a supporter in the English Crown's coat of arms (one of two supporters, along with the traditional English lion). The red dragon is often seen as symbolising all things Welsh, and is used by many public and private institutions. These include the Welsh Government, Visit Wales, and numerous local authorities including Blaenau Gwent, Cardiff, Carmarthenshire, Rhondda Cynon Taf, Swansea, and sports bodies, including the Sport Wales National Centre, the Football Association of Wales, Cardiff City F.C., Newport Gwent Dragons, and London Welsh RFC.