Gareth Miles (19 April 1938 – 6 September 2023) was a Welsh-language author, playwright, teacher and political activist. He was a founder and former chairman of Cymdeithas yr Iaith Gymraeg (the Welsh Language Society) and played a pivotal role in the Welsh language rights movement. A Marxist, he was also chairman of the Communist Party in Wales. Journalist Martin Shipton described him as "one of the most influential figures in the 20th century Welsh language movement."

Miles was born in Caernarfon on 19 April 1938 and was brought up in the nearby village of Waunfawr. His father was from Pontrhydyfen, a village that had a significant influence on Miles throughout his life. He had two sisters, Lisabeth and Gill.

Miles attended Bangor University before becoming a teacher of French and English at schools in Amlwch, Dyffryn Nantlle, and Ysgol Morgan Llwyd, Wrexham. He later became a headteacher at Ysgol Dyffryn Nantlle. He eventually settled in Pontypridd with his family.

Miles gained early prominence in May 1962 when he became the first person to be fined for demanding equal status for the Welsh language. Money was taken from his pocket whilst in custody to pay a £1 fine that he had no intention of paying, which had been imposed for giving a fellow student a lift on the crossbar of his bicycle some six months earlier. This act of civil disobedience was symbolic, as many Welsh nationalists viewed English-only court summonses as a symbol of English state authority and the subordinate status of Welsh within that system.

In the August 1962 issue of Welsh Nation, Miles encouraged readers (in English) to follow his example and attend a meeting of a new language movement in Pontarddulais that August - the first meeting of what would become Cymdeithas yr Iaith Gymraeg. The organisation was founded on 4 August 1962 following a radio lecture by Saunders Lewis titled "Tynged yr Iaith" (The Fate of the Language).

Miles served as chairman of Cymdeithas yr Iaith between 1967 and 1968. In reflecting on his leadership, he took pride in preserving the unity of the movement and defending the policy of non-violence. He was instrumental in the sign-painting campaign that involved defacing English-only signage, defending it by saying: "Certainly, we had fun with it. Every time we see a Welsh sign, Cymdeithas can congratulate itself."

After his teaching career, Miles became the national organiser of Undeb Cenedlaethol Athrawon Cymru (UCAC), the Welsh teachers' union. Ioan Rhys Jones, UCAC's current General Secretary, described him as "an exceptionally effective national organiser" who had "a thorough knowledge and understanding of Wales" during the early days of discussions on devolving education.

Miles was also Chairman, Secretary and Writer and Editor of Tafod y Ddraig (The Dragon's Tongue) over the years.