Short answers, pulled from the story.
The Louvre Palace was originally built as a military fortress in 1190 by King Philip II of France to defend the right bank of the Seine against the English-held Duchy of Normandy. The castle was completed in 1202 and included a cylindrical keep, the Grosse Tour du Louvre, standing thirty meters high with external walls four meters thick.
The Louvre Museum first opened in 1793. Before becoming a museum, the Louvre Palace served intermittently as a royal residence between the 14th and 18th centuries, and at various times as a fortress, prison, archive, and treasury.
The Louvre Pyramid was designed by American architect I. M. Pei. It opened to the public on the 29th of March 1989 as part of President François Mitterrand's Grand Louvre project, announced in September 1981.
The Tuileries Palace, built for Catherine de' Medici starting in 1564, was set on fire during the Paris Commune on the 23rd of May 1871. Its main block was demolished in 1883. The Pavillon de Flore and Pavillon de Marsan, which once marked its southern and northern ends, are now considered part of the Louvre Palace.
The Louvre Palace has a total floor area of 244,000 square meters. Of that, 51,615 square meters are devoted to public exhibition space, spread across three wings named after Maximilien de Béthune Duke of Sully, the first museum director Vivant Denon, and Cardinal Richelieu.
The oldest surviving section of the Louvre Palace, the Lescot Wing, was designed by architect Pierre Lescot and sculpted by Jean Goujon. Francis I formally commissioned Lescot in 1546, though stone deliveries indicate work had begun in December 1545. The wing was built under both Francis I and his successor Henry II.