The PCs first met Mariano when he stepped in to stop Sybil Drear from killing them during a confrontation over the Orien signet ring. Presumably he had followed the PCs (or Drear) without being detected (invisible?). He is affiliated with House Elmaro in some way.
His demeanor is confident, yet friendly. He seems like he knows he is always the smartest (and probably most powerful) man in the room.
Mariano has become the PCs contact with House Elmaro since their falling out with Sybil Drear. He gave them the assignment of supervising the transaction in the sea caves. He has since contacted the PC’s and claimed that the shitstorm that went down in the sea cave was not Elmaro’s fault. He is looking into it and will let the PC’s know if he discovers anything.