Bartholomew is a fallen angel and Naomi's former protege. He is currently assembling his brethren and may be the new leader of the angels. Currently he is searching for Castiel since he and a majority of his fellow angels blame him for their situation.
He makes his first appearance in I'm No Angel. He and his fellow fallen are manipulating a devout religious group into convincing people to let angels into their bodies. They achieve this through online podcasts that are viewed by deeply religious people, who subsequently allow angels to possess them.