Sir William Siemens (1823-1883) Carl Wilhelm Siemens (April 4th 1823 with Lenthe, Germany - November 19th 1883, Great Britain) was a Engineer English originating in Germany, brother of Werner von Siemens, inventor and creator of processes for the manufacture of steel.

It was born in Lenthe, in Germany and emigrated in England in 1844. Thereafter, it directed the English branch of the company of Siemens & Halske. It obtained British nationality in 1859 and was made knight in 1883.

It is famous for the development of the hearth with reheating of gas called Siemens furnace, which it made patent in 1856. This revolutionary furnace was used by Pierre-Emile Martin thereafter for the refining of the Acier: Martin-Siemens process called sometimes Siemens Martin process or even proceeded Siemens (see History of the production of steel). It was also one of the pioneers of the electric energy utilization and one of the most important personalities of Great Britain in the field of science and the Ingénierie.