The Unicorn

Medieval iconography, seen here in a book of medicinal plant remedies, often depicts the unicorn in the company of a lady whose purity it shares.
The unicorn is a minor ancient motif which developed fully in the Middle Ages. This is true of almost all beings in mythology: remember that the representation we have of it is the fruit of a long evolution, of innumerable variants and reappropriations. The fantasy we read is just one further step in building this great imaginary bestiary.