Briars is characterized as a unhygienic, crazy, old prospector who has resorted to grave robbing in his pursuit of treasure. He is over obsessed with an unspecified Treasure and the map that will lead him to it. This obsession has caused him to lose his family, his business, and most of his mind. It is also implied through conversation that his father left him which might also be a cause of his lack of sanity.
Briars has a history of working with Bill Williamson, but is largely removed from the gang lifestyle due to his pursuit of treasure. It is this history which Marston exploits to gain entrance to Fort Mercer in "The Assault on Fort Mercer".