Although Contax is now considered a brand of cameras, it started out as the name of one model of 35mm rangefinder camera.
The Contax camera was introduced in 1932 by the Carl Zeiss Foundation to compete against the first 35mm camera, Leica. In order to produce 35mm cameras, Carl Zeiss had bought a number of smaller camera companies and combined them to form Zeiss-Ikon. The Contax never had as many variants as the Leica. There were three major models introduced during production: Contax I, Contax II (world's 1st combined range/viewfinder, and Contax III (built-in light meter). For a long time, Contax and Leica were quite competitive with one another, each carving out most of the early 35mm camera market share. Some would consider Leica's camera designs superior, while others would point out that the Contax lenses were superior, due to Zeiss's extensive lens manufacturing experience. Contax II's top shutter speed of 1/1250 is odd, and was probably only designed so that they could claim superiority to Leica's top shutter speed of 1/1000. Interestingly, both companies, as well as others, made lenses to fit both cameras.
Eventually, as Leica and other companies continued to make improvements to their camera designs, Contax became more and more dated. Zeiss didn't modernize their design past the Contax III model, probably in part due to the fact that the Carl Zeiss factories were seized by the Soviet Union at the conclusion of WWII. The Contax rangefinder camera died a quiet death, while the name lives on as a well-respected brand.
In the following years, the Contax name was used in a variety of SLR models. Though some of these cameras made some innovations, they were never able to dominate the market in the way that the rangefinder camera ever did.
The Contax name is carried on a variety of high quality "boutique" 35mm SLR cameras (the Yashica and Contax 35mm SLR lens mounts are shared) and a recently released autofocus medium format camera. The Contax AX is a unique camera in that it achieves autofocus not by moving the lens (as is normal) but by moving the film plane. This concept is shared by the early-post-war Mamiya Six medium format camera, though of course the Mamiya is manual focus.
Interestingly, Nikon's first camera was a copy of the Contax rangefinder. Somewhat annoyingly, they got the lensmount slightly wrong so that lenses made for Contax fit the Nikon rangefinder and vice-versa, the focusing mechanism is slightly off. Nikon rangefinders continued to innovate, soon eclipsing the original. These classic Nikon rangefinders are collector's pieces, fetching many thousands of dollars; much more than the Contax originals. Interestingly, Nikon has recently reissued a rangefinder camera, as well as some compatible lenses.