He was born as Niels Olsen (Olufsen) in the city of Stavanger in Norway in 1655 and was half Norwegian and half Dutch. It is uncertain when the Norwegian Niels Olsen (in Dutch `Cornelis Roelofsz') emigrated to the Dutch Republic and changed his name to Cornelis Cruys (Kornelius Krøys or Cornelis Cruijs). However, according to several municipal sources, Cruys lived in Amsterdam for at least eighteen years before he joined the Russian Navy.