Barth

Septon Barth is an unseen character in Game of Thrones. He is not expected to appear in the show, being long dead by the time it begins. He was Hand of the King to Jaehaerys I Targaryen.

Biography
When Jaehaerys became king, the crown was at war with the Faith Militant. Jaehaerys believed that harmony between the crown and the Faith would be good for the realm, and Barth reached an accord with the High Septon. While the crown defended the Faith, the Faith would remain peaceful and withold codemnations of the incestuous practices of the Targaryens. The Faith Militant was disbanded as a result.

Reference

 * "The Faith Militant (Histories & Lore)"