John Lasarus Williams (29 October 1924 – 15 June 2004), known as John L, was a Welsh nationalist activist.

Williams was born in Llangoed on Anglesey, but lived most of his life in nearby Llanfairpwllgwyngyll. In his youth, he was a keen footballer, and he also worked as a teacher. His activism started when he campaigned against the refusal of Brewer Spinks, an employer in Blaenau Ffestiniog, to permit his staff to speak Welsh. This inspired him to become a founder of Undeb y Gymraeg Fyw, and through this organisation was the main organiser of Sioe Gymraeg y Borth (the Welsh show for Menai Bridge using the colloquial form of its Welsh name).^[1]

Williams also joined Plaid Cymru. He was a long-serving councillor on Gwynedd County Council, and was twice the party's candidate for Anglesey, at the 1970 and 1979 general elections.^[1][2]

Williams later worked at Bangor Normal College, lecturing in Welsh. He wrote a number of books, on history, the Welsh language, and also his autobiography.^[1]