Iolo Morganwg (or Morgannwg in modern spelling) was the bardic name of Edward Williams (Llancarfan, Glamorgan, Wales 1747-1826), an influential antiquarian, collector and literary forger. The name is Welsh for “Ned of Glamorgan”.
Edward Williams spent his working life as a stonemason. It is as Iolo Morganwg that he is remembered, chiefly for his role in (re)creating modern bardic ritual and philosophy. He founded the first Gorsedd, Gorsedd Beirdd Ynys Prydain, at a ceremony in 1792 at Primrose Hill, London. He also authored fairly substantial works (most of which are now considered forgeries) claiming that the ancient druidic tradition had survived intact in Wales, despite the Roman conquest, Christianity, the persecution of the bards under Elizabeth Tudor, and other adversities. Iolo’s philosophy represented a fusion of Christian and Arthurian influences, a proto-romanticism comparable to that of William Blake, the revived antiquarian enthusiasm for all things “Celtic”, and such elements of bardic heritage as had genuinely survived among Welsh-language poets. Part of his aim was to assert the Welshness of the South, particularly his home region of Glamorgan, against the prevalent idea that North Wales represented the purest survival of Welsh traditions.
He was addicted to laudanum for most of his life, which may have affected his mental condition.
Iolo was the author of the “Druid’s Prayer” or “Gorsedd prayer” (Gweddi’r Derwydd or Gweddi’r Orsedd in Welsh), which is still a staple of the ritual of both gorseddau and Neo-Druidism. His metaphysics outlined a theory of concentric ‘rings of existence’, proceeding outward from Annwn (the Otherworld) through Abred and Ceugant to Gwynfyd (purity or Heaven).
Among his writings was Cyfrinach Beirdd Ynys Prydain, or “The Mystery of the Bards of the Isle of Britain” (1829), a treatise on Welsh metrics.
A Welsh language school in Cowbridge, Ysgol Iolo Morgannwg, is named after him.
I found this guy in the wikipedia under “Notable literary figures addicted to laudanum”