George Churchward’s Star class locomotives, launched in 1907, set the pattern for the engines that would haul GWR’s glamorous passenger expresses during the golden age of steam. Examples of the Castle and King class developments of 1923 and 1927 remained in service until the end of steam in the region. This analysis provides an illustrated technical evaluation of the three locomotive designs and details of their allocation and work on the network up to the 1960s.