Saint Twrog was a 6th century Welsh saint who founded the church at Maentwrog. It is believed that Twrog was the son of Ithel Hael o Lydaw of Brittany. He was also the brother of Saint Tanwg of Llandanwg, Saint Tegai of Llandegai and Saint Baglan of Llanfaglan and Baglan [1].
There are two other dedications to Saint Twrog at Bodwrog in Anglesey (St Twrog's Church, Bodwrog) and at Llandwrog (St Twrog's Church, Maentwrog). When Twrog first arrived in the village the valley was very marshy, which provided him with the wattle that he would have needed to build his cell. Out the church near to the belfry door is a large stone known as Maen Twrog (maen being the Welsh for stone). Twrog is reputed to have thrown the stone from the top of Moelwyn crushing a pagan altar in the valley below. It is said that his handprints can still be seen in the stone. The parish of Maentwrog gets its name from this stone[2]
The village name Maentwrog literally means "Twrog's stone". It is said that if one rubs this boulder one is fated to return to the village in the future.
However the name was already in existence at some time before this as it is said in Welsh mythology found in the Mabinogion that Pryderi was killed at the Glaslyn river and in Maentwrog is he buried. The boulder supposedly hurled by the giant is the one said to mark Pryderi's grave.