Not much is known about Gwrtheyrn as he is only seen in his granddaughter's family tree. Despite him having an Irish last name, his first name suggests that he may also be of Welsh ancestry, unlike his wife who has an Irish first name. According to Gwrtheyrn's Sim DNA in SimPE, his hair color was red before it turned grey. When viewing his age data in SimPE, he had 20 days left before dying of old age. Gwrtheyrn's facial structure is very similar to that of Goopy GilsCarbo.