Complex sentence: Finally, an Hidalgo was a minor Spanish title (roughly equivalent to a Baronet now obsolete); in the novel, it was the title Alonso Quijano had even before becoming Don Quijote.
Split into simpler sentences: Finally, an Hidalgo was a minor Spanish title (roughly equivalent to a Baronet), now obsolete. In the novel, it was the title Alonso Quijano had even before becoming Don Quijote.