Sometimes a design is a classic because it's so simple. That's the Fritz Hansen Dot stool by Arne Jacobsen.
The Dot, aka the model 3170, was developed by Fritz Hansen in the 50s (1954), but as a three-legged stool. It was adapted in 1970 to the design that's available today. Those legs are made of steel, while the seat is made of ash, coloured in a variety of shades, some of which are pictured above.
Looks good, pretty useful too. £191 gets you one.