Sigmundo is a dragon, the scion of SuGar, otherwise known as the Great Serpent of the Pyrenees. SuGar is the consort and companion of Mari, the chthonic goddess of the Basques, although she isn't Sigmundo's mother.
Able to change shapes, and gifted with impressive magical power, Sigmundo claims to be Vibria's grandfather.
Following a deal with Antonio, he gained access to hermetic books.
When they discovered the deal's implication that he had access to hermetic secrets, this prompted the magi of Andorra to offer him to join the order, which he did, under a human guise.