Who invented razor blade?

If you mean the disposable razor blade, it was patented by King Camp Gillette. His idea was the first of the "loss leader" model which is still in use today. The idea is to have a popular idea, provide the base product at a loss...but provide the replacement item for the product at a huge profit.

This idea is prevalent with many products today such as razors (of course), hair appliances, and the Barbie doll.

See the related links.