Banshee is strong, perceptive, tough and looks more sinewy than bulky. He's going bald, but he doesn't know why; maybe he ate something bad. He's taken it out on his wife and kids. He killed his previous wife for accidentally burning his hair. 
One month prior to the arrival of the Prisoner, one of Larsen's men freaks out and Larsen shoots him, then offers the body to the Jackals. Larsen (and the Baggers) then become allies with Banshee (and the Jackals), both wanting to get into the dome.
By the time the player arrives in Boulder Dome, Banshee is in a Mexican standoff with Larsen, as both want to get in to the Dome and neither wants the other to live after that.
During the intro to Fallout: Brotherhood of Steel 2, on your way down to Texas, you and your squad are suddenly attacked by a group of raiders. These raiders, however, are dressed in power armor and have massive weapons. Your squad is caught completely flat-footed. As a blast from a plasma cannon knocks you down, the leader of the raiders, Banshee, approaches and strips off the players armor and leaves them for dead.
Later at Fort Worth, the player encounters Banshee again as a boss character. Banshee will kill Cyrus, whom the player is currently fighting. Afterwards the player will then fight Banshee. When Banshee is defeated, the player will threaten him, and Banshee gives the player a key to the Vault in Lone Star, and says all the answers are there. But before he can tell the player who's behind it all, he explodes...