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Leica had been making 35mm cameras since the 1920s and defined the category, but in 1948 Nikon came out with a rangefinder that was more advanced. In many ways it combined the best features of Contax and Leica, with a combined view/rangefinder, removable back (you loaded a Leica from the bottom), and bayonet lens mount. In 1954, with the M3, Leica closed the gap. (You still loaded from the bottom, though.)

The Leica M3 has a bayonet mount (the M mount), a combined view/rangefinder and, unlike the Nikon S, a quick-lever film advance, although that was matched by Nikon with the S2, which also came out in 1954.

Here's an early ad that ran in the July 1954 issue of Popular Photography:

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And another ad that ran in Sept. 1955:

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Here's a fold-out M3 brochure, shown broken up into sections:

Leica M cameras stayed much the same all the way into 2007 with the M8, one of which I owned but have since sold. In 1971 the M5 got a built-in exposure meter, but, of course, no Leica rangefinder ever got auto-focus. (Nikon completely lost interest in professional-level rangefinders after the Nikon F came out in 1959.)

Here's my M8:

The M3 shown at the top belonged to my brother-in-law who bought it used in the 1960s I think. Its obvious hard use mostly came from him—as far as I know, it was the main camera he used while his family was growing up. (He had very good taste, as his other camera was a Hasselblad.)

His Leica's serial number, 816597, puts its date of manufacture at March 1956 according to CameraQuest's list. Note that it has a frame-line selection lever, which the original model shown in the ad didn't have.

I only shot one roll of film with this M3, although I took lots of pictures with my M8 while I had it.

Leica rangefinders are much loved by photographers who use them or once did, and mostly ignored by everyone else. I enjoyed my M8, but finally got tired of its limitations. The only thing I miss about it is that it's small and takes great pictures. My other cameras are one or the other but not both.