The Laocoon discovered in Rome in 1506 is a marble sculpture presumed to be of the crushing to death by a sea serpent of the Trojan priest Laocoon and his son(s) (see Virgil, Aeneid, 2, 40-56 and 199-231). It was bought by Pope Julius II and moved to the Belvedere in the Vatican, where it has remained, apart from the period between 1797 and 1816 when it was in Paris until its return to Rome under the Treaty of Tolentino. It was seen as being the piece mentioned by Pliny as a work to be preferred above all paintings and sculptures (Pliny, Natural History, XXXVI.4.37). It has generated a large volume of writing both on its realism and its expression of emotion, and also on the attempts which have been made to restore it. Ruskin at Works, 4.120 gives an unfavourable opinion of it, but refers the reader to Schiller and Winckelmann for the opposite view. Cook and Wedderburn refer in a footnote to that passage to the oddity of Ruskin not mentioning Lessing's Laokoon of 1766, perhaps the best known of the writings on the subject ( Works, 4.120n).
For Reynolds it is listed along with the Apollo Belvedere, the Venus de' Medici, the Moses of Michelangelo, 'and many others', as an example of art which 'may be said to have accomplished its purpose'. ( Reynolds, Discourses, p. 178)
For a list of references see Haskell and Penny, Taste and the Antique, pp.243 ff.
See Ruskin and the Italian School.