William Williams (1717-1791), though his exact birthdate was unrecorded. The occasion is being celebrated tomorrow in his home country with a broadcast service filmed at the church where he was buried, described in this article in the South Wales Guardian.
Williams published two books of his hymn texts, Halleluiah (1744) and Y Môr o Wydr (1766) which became very popular in Wales. He also released two volumes containing 121 of his texts translated into English: Hosannah to the Son of David (1759) and Gloria in Excelsis (1771) -- later combined into one volume in 1859.
Of course, Williams' best-known hymn today is Guide me, O thou great Redeemer (originally Jehovah), and I believe I can safely say that it is not "better known today as the rugby anthem Bread of Heaven" in this country, at least. Though it was written and translated in the eighteenth century, the tune nearly everyone sings today, CWM RHONDDA was not written until 1905. As you can see from the timeline chart at Hymnary.org (scroll down), that tune would lead to even wider use of the text in twentieth-century hymnals.
So, for more than 150 years, it was sung to other tunes, including GUIDE ME by George William Warren, ZION by Thomas Hastings (apparently one of the more-utilized nineteenth-century tunes for the text), PILGRIM by Albert Lister Peace (which certainly sounds like it was written by the composer of ST. MARGARET), and PILGRIMAGE by George Job Elvey (for a little Victoriana), among others. I'm not sure that any of them would have become a rugby anthem.
Nevertheless, let's remember the important work of William Williams, the "Watts of Wales" whose hymns spread from his own country around the world, including one which remains the favorite of many.
Eight Years Ago: Washington Gladden