Vo was a man from Chedesh who was the first Returned on Nalthis.
Like most Returned, he died a week after returning, leaving his wife to bear him an heir. His wife would later rule as queen and set up the royal lineage which eventually went down as far as the Idrian royal family e.g. Siri. According to the discussion in Warbreaker it is indeed possible for any Returned to bear children, but only when one has special knowledge which has not been revealed yet, although the priesthood of the God King are aware of how to do so.
While the priesthood are aware of how to have a Returned successfully give birth, Siri assumes that it is impossible and that the story of Vo having fathered a child was made up in order to legitimize the royal line of Hallandren Vasher mentions to Nightblood that the royal locks Vivenna exhibits are proof that she is indeed descended from a Returned and that she has a piece of a Returned in her.
He Returned and had the Five Visions whilst travelling the coast of Hallandren by boat. His shipmates founded the kingdom of Hanald in the lands of the Pahn Kahl.
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