On Saturday 15 September 1984 a memorial stone was unveiled by a Prifardd (chaired or crowned bard) to mark the site in the churchyard at Talley where a deeply-rooted tradition asserts that the poet Dafydd ap Gwilym (c.1315 - c.1350) lies buried.  However, for many centuries, the rival claims of Talley and Ystrad Fflur have been debated as  his burial place.  It is generally regarded that he was born at Brogynin, Penrhyn-coch (Llanbadarn Fawr parish), Ceredigion.

He is regarded as one of Wales' foremost poets and was responsible for popularising the metre known as the "cywydd".  His main themes were love and nature, with his work full of his own feelings and experiences and the troubadour poetry of Provençal, seen as a significant influence on his work.  Around one hundred and seventy poems of his have survived, although many later ones are attributed to him.  

On 15th September 1939, the regular passenger service on the Ffestiniog railway ceased to operate. 

The Ffestiniog Railway was opened as a horse-drawn tramway in 1836 to transport slate from the Blaenau Ffestiniog quarries to the harbour at Porthmadog.  The increase in cargoes (100,000 tons by the 1890s) led to the introduction of steam locomotives from the middle of the 19th century.  However the subsequent decline in the demand for slate saw the complete closure of the line.  However, in 1954, a group of enthusiasts stepped in to reopen the line and with twisting turns, steep gradients and a complete spiral, the Ffestiniog is now regarded as one of the U.K's most spectacular narrow-gauge lines.  

The Gleision Colliery mining accident occurred on 15 September 2011 at a drift mine in the Swansea Valley of South Wales.

The accident occurred while seven miners were working underground with explosives.  An initial explosion caused the tunnel in which the miners were working to begin to fill with water.  Three of the men managed to escape but the rescue operation to find the remaining four men found them dead the following day. This disaster was the worst to occur in Wales for three decades.  

Edward Jeffrey Hamm (15 September 1915 – 4 May 1994) who was born in Ebbw Vale was a leading British Fascist and supporter of Oswald Mosley.  

Born on 15th September 1846, William Jones from Pencnwr Farm at Dinas was a Welsh soldier in the American army. He emigrated to the United States in 1870, where he found work in Chicago as a coachman before joining the Cavalry and was killed fighting with General Custer at Little Big Horn in June 1876 

Another Welshman escaped the same fate was Lord Dunraven of Dunraven Castle in Southerndown, near Bridgend.  He had been hunting for elk with  Buffalo Bill Cody when he was invited by Custer to join an expedition against the Native Indians.  However, fortunately for him, he received the invitation too late.  

Look Back in Anger, released on 15th September, is a 1959 film starring Richard Burton and Edith Evans and directed by Tony Richardson. 

It is based on John Osborne's play of the same name about a love triangle involving an intelligent but disaffected young man, his upper-middle-class, impassive wife and her snooty best friend, with the Welsh lodger, attempting to keep the peace.