Hugo von Hofmannsthal's fame is inextricable from that of Richard Strauss, with whom he created seven operas, at least three of which can be counted as the most successful and enduring of the 20th century. His librettos, filled with subtle characterization and masterful symbolism, are among the very few that are independently enjoyed as literature, particularly in his native Austria. His family encouraged his writing from an early age, and even in his teens his poetry was widely published and admired. After a brief dry period in his twenties, he re-emerged with a reinvigorated passion for the theater, particularly as an art form that combined poetry, drama, and frequently music. He drew new inspiration from Greek drama, particularly the tragedies, and it was one of these that began his association with Strauss, who, on seeing a performance of Hofmannsthal's 1903 adaptation of Sophocles' Electra, suggested it as material for an opera; their finished work premiered in 1909. Two years later, they created Der Rosenkavalier, followed by Ariadne auf Naxos (1912, revised in 1916) and Die Frau ohne Schatten in 1919. The next year, he and Max Reinhardt founded the Salzburg Festival, a theater to celebrate both music and drama. His next Strauss collaboration was Die Ägyptische Helena (1928), followed by Arabella, which premiered in 1933, after his death. He had also begun the libretto for Die Liebe der Danae, which was completed by Joseph Gregor. His plays had also provided libretti for other composers' works, including Tcherepnin, Brehme, Wellesz, and Varèse, but it is his association with Strauss that created the greatest impact on the musical world. Fortunately for music historians, he and Strauss rarely met in person and instead corresponding in letters, so much of their interaction has been recorded for posterity.