This year marks 75 years since the publication of the first Penguin paperback, which initially went for sixpence.
From the BBC:
"With the average hardback costing the equivalent of a week's rent, in the 1930s, a good contemporary read for most was absolutely unobtainable.
"That is until Penguin's founder, Allen Lane, brought out the first sixpenny paperbacks in the now iconic Penguin colours of orange for fiction, green for crime and blue for biography."
And it was Allen Lane who accidentally created the rarest Penguin -- in the middle of the night -- and it was a collection by a cartoonist.
The rarest Penguin book? A collection by the cartoonist Bob Siné titled MASSACRE. Penguin collector Steve Hare has his copy.
"Published in the 60s, MASSACRE glories in Siné's obsessions with the Catholic church, nuns and mutilation.
"Steve says: 'Allen Lane took offence to it, so he sneaked into his own warehouses at night and removed every copy that hadn't been sold and either burnt, buried or composted what was left.
"'So, a few of these were sold but no one knows how many.'"
Related: I covet these Penguin book cover mugs. Image from the Australian Until Company site.