Final answer:
Richard Wagner is the opera conductor celebrated for his outstanding orchestration in both tone poems and operas, as well as his longstanding song composition throughout his career.
Step-by-step explanation:
The Renowned Opera Conductor and Composer
The opera conductor known for using brilliant orchestration, initially in tone poems and later in operas, while also composing songs throughout his long career, is Richard Wagner. Wagner's innovations in opera were profound, from the development of the leitmotif to the seamless flow of his music dramas. He is also credited with the invention of the orchestra pit to enhance the auditory experience of opera goers. His approach to opera, with its rich orchestration and complex harmonies, pushed the boundaries of the music of his time, squarely placing him in the post-Romantic era, where he and composers like Mahler explored the limits of Romantic musical techniques.
Wagner's reputation as a composer of operas is paralleled the innovations he brought to the art form, taking the concept of the Gesamtkunstwerk, or total work of art, to remarkable heights. His operas, such as 'The Ring of the Nibelung', 'Tristan und Isolde', and 'Parsifal', continue to be performed regularly at opera houses around the world.