Major Banks was a member of the military stationed at the Boston Quarantine Zone during the Summer of 2033. He was mentioned in an artifact that Ellie can find in the Left Behind DLC for The Last of Us.
He was Sergeant Winston Asher's commanding officer. Asher wrote a letter of complaint to Banks regarding the number of civilians sneaking through the abandoned mall at Liberty Gardens from the gradually dying Hartford QZ, with many actually being infected and mutating into Runners that Winston was forced to kill. He wanted Banks to provide more patrols and supplies even though they were running low on food. Winston considered Banks incompetent as a leader, complaining in his letter that the Major would only ignore his warning.