The Bulldog and Bird classes were double-framed inside cylinder 4-4-0 steam locomotives used for passenger services on the Great Western Railway. The Bird Class were a development of the Bulldogs with strengthened outside frames, of which a total of fifteen were built. A total of 121 Bulldogs were built new, with a further twenty rebuilt from Duke Class locomotives. Thirty Bulldogs were later rebuilt as Earl Class locomotives and renumbered 3265 (prototype conversion), 3200-3228.