Franz Joseph Haydn was an Austrian composer, called the "Father of the Symphony" and "Father of the String Quartet". He was the most popular composer around that time. His greatness is shown in Mozart's letter when Mozart dedicated his six string quartets KV.387, 421, 428, 458, and 465 to Haydn.
Vienna, September 1, 1785
To my dear friend Haydn,
A father, having decided to send his children out into the wide world, felt that he should entrust them to the protection and guidance of a famous Man who by good fortune also was his best Friend. - Here they are, distinguished Man and dearest Friend, my six children. - They are, to be truthful, the fruit of long and laborious efforts; however, the hope given me by various Friends that my efforts will be at least somewhat rewarded encourages and flatters me to think that this offspring will be of comfort to me someday. You yourself, dearest friend, told me of your approbation of them during your last Visit here in our Capital. This acceptance gives me the courage to commend them to you and makes me hope that they would not be completely unworthy of your favor. May it please you to welcome them kindly and to be for them a Father, Guide, and Friend! From this moment on I hand over to you all my rights in them, begging you, however, to consider with indulgence their flaws, which a Father's uncritical eye may have overlooked, and in spite of them continue your generous Friendship toward one who so greatly appreciates it, while I remain, Dearest Friend, with all my heart, your most Sincere Friend,
W. A. Mozart