The modern, heated hair curling iron was invented by Frenchman Marcel Grateau in 1872. He used metal tongs as a curling iron that were heated over a gas burner. The style he created with the tongs was called the Marcel Wave (Marcelling).

Grateau's curling tongs operated like a pair of scissors. The user opened the handle, inserted the hair, and closed the tongs to create a crimp. A long piece of hair could be wrapped around the tongs to create a curl. This system required the user to keep the handle closed while the hair was curling. Modern-day curling irons have employed a spring-loaded handle that holds the hair against the iron.

It is believed that the Marcel Wave marked the beginning of hairdressing. It directly accounted for a contemporary shape, with many women then flocking to hair salons to get the Marcel Wave.

More Info: en.wikipedia.org