Final answer:
Louis XV put Le Panthéon up as a gratitude to King Louis XIV, who centralized the government in France and ruled with absolute power.
Step-by-step explanation:
King Louis XIV, also known as the 'Sun King,' is who Louis XV put Le Panthéon up as a gratitude to. Louis XIV centralized the government in France and ruled with absolute power. He used art and architecture in the service of the monarchy and established the Royal Academy of Fine Arts to control matters of art and artistic education.