A soldering iron is a hand tool used in soldering. It supplies heat to melt solder so that it can flow into the joint between two workpieces.
A soldering iron is composed of a heated metal tip and an insulated handle. Heating is often achieved electrically, by passing an electric current (supplied through an electrical cord or battery cables) through a resistive heating element. Cordless irons can be heated by combustion of gas stored in a small tank, often using a catalytic heater rather than a flame. Simple irons less commonly used today than in the past were simply a large copper bit on a handle, heated in a flame.
From Kurtz Ersa
Today, it is difficult to say who first discovered how to "glue" metals. One thing is certain; the goldsmiths of ancient Egypt knew how to join gold more than 5,000 years ago. Their colleagues in Troy were also masters of soldering long before the ancient Teutons could even dream of such handicraft. Soldering "came of age" when tin was discovered as a soldering metal - and that was 4,000 years ago!
From then on, the world´s soldering technology was on its way upwards. It first spread around the Mediterranean. The Cretans showed it to the Etruscans, who then taught it to the Romans, Tunisians and Spanish, followed by many others, including the less developed cultures of the time - the Swiss, Bohemians, Hungarians, Teutons and Scandinavians.