The Roswaal family is a noble magician family in Lugunica. The family got serperated after the Sealing of the Witch and only the Original Roswaal was the last member of the Family, hearing this, he made a contract with Echidna and created a wager that everytime a Roswaal member died, that the soul of the Original one will pass down to the recenst.
Through out thousands of years, the original Roswaal's soul kept passing down to the youngest member of the family. Also, the Roswaal's had a strong connection with Echidna. One of the previous Roswaal's even wanted to kill Volcanica to free Echidna's soul and marry her. Although Echidna had no intrests in the Roswaal's, she used them as help to free her.
After Jens and Emilia killed Echidna, Roswaal became furious and left the Mansion. However, he made his appearance during Face to Face with Death and apologized to Jens.