Some authors who have written classics are William Shakespeare, Geoffrey Chaucer, Miguel Cervantes, Niccolo Machiavelli, Lao Zi (Lao Tzu), and Confucius.
Classics in this sense make up what some call a canon of world literature. The question of what belongs in the canon of Western literature and art is a matter of much dispute.
Most "classics" are at least 95 years old, and most authors of classics have been dead for at least 70 years, but sometimes we press the word into use to praise newly-created works.
Most classic books are in the public domain due to their age (except those few books for which a government has granted a perpetual copyright), and are freely available online from Project Gutenberg at http://promo.net/pg