Most souls are not new, they are not in the world for the first time.
Almost every person bears the legacy of previous existences.
Generally one does not obtain the previous self again, for the soul manifests itself in different circumstances and in different situations.
What is more, some souls are compounded of more than one single former person and share parts of a number of persons.
–Rabbi Adin Steinsaltz
From The Thirteen Petalled Rose by Rabbi Adin Steinsaltz