The leading Welsh bibliographer of the century, known as 'Gwilym Lleyn'. He followed his father's trade as a weaver, but began preaching at 19. His itinerancy enabled him to search for books in many parts of Wales and he began to publish his Cambrian Bibliography in the CM monthly Y Traethodydd in 1852. After his death the work was edited by Daniel Silvan Evans and published in 1869 as a volume of over 750 pages, an astonishing achievement at a time when no major libraries existed in Wales. He edited Yr Eurgrawn Wesleyaidd 1842-1845 and 1852-1856.