Paperback novels didn’t really exist prior to about the mid 20th century. Before that, books were big, heavy, expensive things sold to rich people, generally reprints of older works, and genre works like science fiction and romance were sold in pulp magazines of low repute. Penguin–as in the publishing company, now known as half of Penguin Random House–was the first to successfully change that, with its introduction of cheap, mass produced books sold outside of traditional bookstores.