If you want to understand the world of Richard Strauss, circa 1919, the book to read is Stefan Zweig’s “The World of Yesterday”, which is a combination of autobiography, social commentary, and cultural anaylsis. If you can find it, you might also try Lotte Lehman’s “Five Operas and Richard Strauss”.
A clarification: the leitmotiv I’m referring to comes initially when the Emperor is describing how he wounded his favorite falcon, out of some weird fear or jealousy, at the time he captures the gazelle, which turns into the Empress. It is a small phrase from the long, opulent melody associated with the Emperor as hunter.