A razor is an edge tool primarily used in shaving.
In its simplest form, a razor is a blade attached to a handle. Razors have been identified from Bronze Age Britain. These were made of bronze and were generally oval in shape, with a small tang protruding from one of the short ends.
Straight razors (also called cut-throat razors because of their potential lethality) with open steel blades were the most commonly used razors before the 20th century. However, they are now chiefly used by barbers.
The safety razor was developed in 1875 by the Kampfe Brothers, the first safety razor manufactured in the United States was known as the Star. Early razor blades needed continual sharpening, becoming worn out and expensive; however many still consider them superior. They developed a type of razor along these lines.
In 1901, the American inventor King Camp Gillette, with the assistance of appropriately named William Nickerson, invented a safety razor with disposable blades. Gillette realized that a profit could be made by selling a razor with inexpensive disposable blades. This has been called the Razor and blades business model, or a "loss leader", and has become a very common practice for a wide variety of products; for example, game console manufacturers will often sell hardware for a loss, then make up for it by collecting a cut of the money made on software sold for the system. To realize his idea, Gillette applied for a patent on December 3, 1901, which was awarded as patent US775134 on November 15, 1904. The company manufactured its first razor in 1903. Gillette's particular innovation for safety razors with disposable blades beat out competitors. Gillette's thin blade was covered by the razor housing, thus protecting the skin against deep cuts. This enabled the majority of people to safely shave themselves for the first time. Prior to this, shaving was often only done by family members or barbers.
Plastic disposable razors and razors with replaceable disposable blade attachments, often with two or three cutting edges (but sometimes with four and as of recently, five cutting edges), are in common use today. Still, the double-edged blade continues to have adherents, for reasons of cost (4-7 shaves from a blade costing as low as US$0.12 vs. as high as US$3.50 for one of the latest multi-blade cartridges), comfort (some find the multi-blade cartridge hard on their skin), and pleasure (those now using the double-edged blades find such shaves, usually done with a shaving brush and shaving cream or soap, to be pleasurable).
Razors are generally marketed in men's and women's versions; the exact difference between the two varies from color only for most cheap disposable razors to completely different design principles. By and large, men's and women's razor blades and disposable razors are interchangeable; however, there is sometimes a difference in ergonomics -- women's razors either have a longer handle for longer reach or a paddle-shaped handle to allow for a lengthwise grip.
Specialized designs also exist, for such things shaving the head or the bikini line.