Which composer is known for establishing the standard for symphony, sonata, and string quartet?

The composer who is recognized for establishing the standard for symphony, sonata, and string quartet is Haydn. He is often referred to as the "Father of the Symphony" and the "Father of the String Quartet" due to his significant contributions that shaped these forms in the Classical period. Haydn's innovative approach to structure, form, and orchestration set foundational principles that later composers, including Beethoven and Schubert, built upon. His development of the symphonic form included the standardization of the four-movement structure, which became a template for future symphonies. Similarly, his work in string quartets helped define the genre, emphasizing interplay among instruments and laying groundwork for the genre's evolution. These achievements highlight Haydn's critical role in music history as a key figure in the establishment of symphonic and chamber music forms.