Fet-Mats or Fat Mats (born Mats Israelsson; died 1677) was a natural mummy found in Sweden in 1719. In 1719, miners in the Falun copper mine found an intact dead body in a water-filled, long-unused tunnel. When the body was put on display, it was identified by his former fiancée, Margaret Olsdotter, as Fet-Mats Israelsson, who had disappeared 42 years earlier. Discovery. On 2 December 1719, miners discovered a dead man in the water-filled shaft known as Mårdskinnsfallet, in a part of the mine that had not been used for a long time.
https://en.wikipedia.org/wiki/Fet-Mats