Razor and Blades
A cheap way in, and a long relationship through the consumable. The shape runs on to printer ink, to coffee capsules, to consoles and their games. As for the textbook version of this model's own story, see the correction above — the more famous the origin, the less likely the originator actually did it. Worth noting too: the way a model becomes the whole industry's the moment the patent lapses happened again, almost identically, in Japan's conveyor-belt sushi. The utility model expired in 1978, and from the following year the competitors poured in.
The myth, corrected
Gillette sold the handle cheap and made its money on blades from the start
While the patent held, from 1904 to 1921, Gillette kept the handle at a full five dollars — rivals' budget versions sold for one. In 1921, the year the patent expired, it reissued the old model at a dollar as the «Brownie» and shifted three million in six months. The turn to earning on blades came after the protection was gone. The most famous story in the history of business models runs the other way round (source: Picker, University of Chicago Law Review, 2011).