Gaius Sextus is the First Lord of Alera. He is married to Gaius Caria. His only child, Gaius Septimus died at the First Battle of Calderon. With no heir apparent, there are many questions as to who shall lead when he dies. Several current Lords are trying to position themselves to lead upon his death while others are just trying to hasten it so they can come to power. Through his network of Cursori, he's kept as informed as possible about such plots.
During Furies of Calderon
Amara informs the First Lord of Fidelias's betrayal. He informs her that she should go to Calderon Valley to follow up on some leads she gathered. After the Second Battle of Calderon and the death of the current Lord of Calderon, Gais promotes Bernard to the position of Lord of Calderon. This leaves Bernardholt without a steadholder. So, Gaius promotes Isana to the position of steadholder, making her Alera's first named female Citizen (all previous female citizens achieved it by either marrying a citizen or winning it through Juris Macto). For bringing in much needed reinforcement from the Marat and saving the Calderon Valley from invasion, Gaius patrons Tavi in the Academy.
During Academ's Fury
Gaius continues to defend the realm. The Canim have been sending massive storms to the southwestern edge of Alera and most of Gaius's focus has been on preventing these storms from making landfall. Eventually, the level of effort required overwhelms him and he goes into a coma-like state. Antillar Maximus is forced to impersonate the First Lord while he is incapacitated.