Sometime about 1746 – the precise date is uncertain – an eight-year old boy, playing by a stream somewhere in West Africa, probably in what is now Sierra Leone, then a haunt of slavers, was abducted and brought to Ynyscynhaiarn, in Gwynedd, North Wales. He was taken to Plas Ystumllyn, either by or for a member of the Wynne family, whose home it was, where he learnt or was taught to speak both Welsh and English. He appears to have been treated as a servant, and was baptized by the Wynne family, either at Ynyscynhaiarn or the mother church at Criccieth.

He was given the name ‘John Ystumllyn’, or, as he was sometimes called, ‘Jack Black’. The child grew to manhood in the Wynne family home, became a proficient gardener, knowledgeable plantsman, and a skilled craftsman. In 1754, when he was about sixteen years of age, his portrait was painted by an unidentified artisan artist, inscribed and dated at bottom: ‘John Ystymllyn 11 May 1754.’