The CH24 by Hans Wegner - widely known as the Wishbone Chair but in Denmark called the Y Chair was commissioned by Carl Hansen and Son and has been in production since 1950.
It is a fascinating design for many reasons.
It followed on, in Wegner's work, from his design of the Round Chair but was to be simpler and cheaper to produce and it is said that it was meant to be a Danish version of the Thonet café chair so lighter in weight than most dining chairs but robust. This does not seem particularly plausible until you look at a Wishbone chair straight on from the back and then you see exactly the profile of that Thonet chair with the hooped shape of the back.
In fact the Wishbone is a clear and deliberate development from the China chairs that Wegner worked on through the 1940s as the Wishbone has a relatively narrow and curved back piece or splat to support the sharply curved back that is set not horizontally but rising up from the front ends in a sweep up to the centre.
This sharply bent back rest has a flat inner face, so it does not stick into the back of the person sitting in the chair and the splat is actually forked - to form a pronounced Y giving the chair its name.