BoCo is a green mixed traffic diesel engine, who primarily works on Edward's Branch Line and occasionally on the Main Line.

BoCo is a tame diesel engine, who is sensible, kind, and has a decent sense of humor. He is also very disciplined, as seen as he stops Bill and Ben from their pranks. Upon his arrival, he was unfortunate enough to be set upon by the mischievous Bill and Ben, when, thinking he had intentionally stolen their trucks, they pretended to be one engine and nearly made his eyes pop out. BoCo is now wise to the tank engine twins' pranks though he still somewhat humors them to a point. He is also good friends with Bill, Ben, Edward, and Duck. He is a true friend and is often willing to stick up for the underdog. BoCo is firm, but fair and friendly in his nature, not being afraid to speak his mind. Even Gordon soon thought of him in high regard when he "saved" him from Bill and Ben's antics. BoCo upholds a more praiseworthy and respectable, likeable image for diesel engines everywhere, being happy to show the more pompous steam engines that diesels have their uses. BoCo helps bring good order across Edward's Branch Line, even occasionally pulling Main Line trains, as Sir Topham Hatt recognizes how versatile he is.