Short answers, pulled from the story.
Johann Joachim Winckelmann was a German art historian and archaeologist born on the 9th of December 1717 in Stendal. He is considered the father of art history and one of the founders of scientific archaeology, the first scholar to systematically separate Greek art into periods and apply the categories of style to the history of art on a large, consistent basis.
Winckelmann's most important work was Geschichte der Kunst des Alterthums, or "The History of Art in Antiquity", published in 1764. It was the first book to trace an organic growth, maturity, and decline across all antique art, covering Egyptians, Etruscans, Greeks, and Romans, and was translated into French in 1766 and later into English and Italian.
Winckelmann's ideal of "noble simplicity and quiet grandeur" became the guiding principle of the Neoclassical movement in the late 18th century. The painter Anton Raphael Mengs spread his ideas in Rome; Jacques-Louis David encountered those ideas through Mengs; Robert Adam adopted them for architecture; and Josiah Wedgwood's Etruria factory popularized them in England from 1782.
Winckelmann was murdered on the 8th of June 1768 in a hotel room in Trieste by a fellow traveler named Francesco Arcangeli. The true motive was never established; the medals given to Winckelmann by Empress Maria Theresa and a possible response to a homosexual advance were both proposed as explanations, but neither was confirmed. Arcangeli was executed a month later by breaking on the wheel outside the same hotel.
Winckelmann held that the goal of art is beauty, achieved when individual and characteristic features are subordinated to the artist's general scheme. A true artist selects from nature only the phenomena suited to his purpose, combines them through imagination, and produces an ideal type in which normal proportions prevail and no single part, such as muscles or veins, disrupts the harmony of the whole.
Winckelmann was homosexual and his contemporaries, including Goethe, recognized this openly. His homoerotic sensibility directly shaped the rhetorical intensity of his aesthetic writing, particularly his descriptions of ancient sculpture. In 1752 he wrote about the "lust" available in Potsdam in terms he compared to Athens and Sparta, and a series of unrequited loves throughout his life deepened his admiration for the male form in ancient art.