Final answer:
Joseph Haydn is called the 'Daddy of String Quartets'. He composed over 80 string quartets and made significant contributions to the development of this genre.
Step-by-step explanation:
The composer known as the 'Daddy of String Quartets' is Joseph Haydn. Haydn was an Austrian composer who played a key role in the development of the string quartet genre. He composed over 80 string quartets, making significant contributions to the form and structure of this type of ensemble music.