Sir Josiah John Guest, 1st Baronet, known as John Josiah Guest, was a British engineer, entrepreneur and politician.

Dowlais is a village and community of the county borough of Merthyr Tydfil, in Wales. At the 2011 census the electoral ward had a population of 6,926, The population of the Community being 4,270 at the 2011 census having excluded Pant. Dowlais is notable within Wales and Britain for its historic association with ironworking; once employing, through the Dowlais Iron Company, over 7,000 people, the works being the largest in the world at one stage.