Dolgoch was built in 1866 by Fletcher, Jennings & Co., but to a very different design to that of Talyllyn. He is an 0-4-0 tank engine with both a back tank (behind the cab) and a well tank (between the frames). The long wheelbase allows the firebox to sit in front of the rear axle, with Fletcher's Patent inside valve gear driven off the front axle, a particularly inaccessible arrangement. In increasingly decrepit condition Dolgoch continued to operate the service single-handedly until 1952 when Edward Thomas became available and was then the subject of a prolonged overhaul between 1954 and 1963.
Dolgoch returned to service in late 1999 after a major overhaul involving firebox repairs and an extensive mechanical overhaul; as part of the overhaul he has been fitted with air braking equipment, the last steam loco on the Talyllyn Railway to be fitted.