An ironmaster is the manager, and usually owner, of a forge or blast furnace for the processing of iron. It is a term mainly associated with the period of the Industrial Revolution, especially in Great Britain.
The ironmaster was usually a large-scale entrepreneur and thus an important member of a community. He would have a large country house or mansion as his residence. The organization of operations surrounding the smelting, refining and casting of iron was labour-intensive, and so there would be numerous workers reliant on the furnace works.
There were ironmasters (possibly not called such) from the 17th century onwards, but they became more prominent with the great expansion in the British iron industry during the Industrial Revolution.