In the 1950s, Hans Wegner made the acquaintance of Dr. Egill Snorrason, an early proponent of ergonomics. Dr. Snorrason pointed out that most chairs offered support too high up on the back, neglecting the lumbar region. Armed with this insight, in 1955 Wegner designed this stunning Swivel Chair for furniture workshop Johannes Hansen:

The back is made of three pieces of teak, finger-jointed and carved into shape.

The seat is leather.

The sheer difficulty of carving the sculpted back meant that this chair was never truly mass-produced. Johannes Hansen, a workshop rather than a large company, produced the chair in small batches or bespoke editions for clients. As a result, it's estimated that no more than a few hundred were ever made. Your chances of spotting one in the wild are slim. If you'd like to see one in person, a pilgrimage to the MoMA or the Vitra Design Museum is in order.