Short answers, pulled from the story.
King Philip II ordered the construction of the Louvre as a fortress in 1190, and the new structure was completed in 1202. The original building was situated on the right bank of the Seine just outside the defensive wall junction.
Francis I ordered the demolition of the old keep after returning from captivity in Spain following his defeat at Pavia in 1528. He formally commissioned architect Pierre Lescot and sculptor Jean Goujon to modernize the site starting around December 1545.
Napoleon III united the Louvre and Tuileries palaces into a single coherent building complex under the direction of Louis Visconti and later Hector Lefuel. The inauguration of these new buildings occurred on the 14th of August 1857, creating the space then called Cour Napoléon.
The Louvre Pyramid underground lobby Salle des Cariatides opened to the public on the 29th of March 1989. This project was awarded to American architect I. M. Pei by newly elected French President François Mitterrand in September 1981.
The Louvre started as a military facility in 1190 and retained military uses for most of its history until plans to create a museum began in 1777. It hosted significant arsenals during the 15th and 16th centuries and stored state collection plans-reliefs from 1697 until they were moved to Hôtel Invalides.