Final answer:
Wagner's masterpiece Tristan und Isolde was influenced by the philosopher Friedrich Nietzsche, whose radical views on religion and nihilism impacted many artists of the period, including progressive composers like Wagner.
Step-by-step explanation:
The philosopher who influenced Wagner's Tristan und Isolde was the nineteenth-century German thinker Friedrich Nietzsche. Nietzsche's challenging ideas about traditional religious views and his concepts on nihilism left a significant imprint on various artists and intellectuals during his time. Wagner, being a groundbreaking composer, found inspiration in Nietzsche's philosophy. Nietzsche's work pushed boundaries and encouraged artists like Wagner to explore complex emotions and controversial themes within their art.Wagner was part of a group of progressive composers, alongside Hector Berlioz and Richard Strauss, who were known for their bold and forward-thinking compositions. These composers did not shy away from challenging the norms of their day, often sparking debates and causing a stir among audiences with their unconventional approaches to music.In conclusion, Wagner's masterpiece Tristan und Isolde was deeply influenced by the bold and revolutionary thoughts of Friedrich Nietzsche, which resonated with the overarching romantic and existential themes that Wagner explored through his musical compositions.