What was Joseph Haydn’s relationship with Wolfgang Amadeus Mozart?

Joseph Haydn and Wolfgang Amadeus Mozart shared a close and mutually inspiring friendship that significantly influenced their respective musical developments.1

The two composers met during Haydn’s frequent visits to Vienna while in the service of the Esterházy family. Their relationship was defined by deep professional respect and personal affection:1

• Mutual Influence: Both composers felt inspired by each other’s work. Mozart credited Haydn with teaching him how to write string quartets, and he dedicated a superb set of six quartets to his "beloved friend". In turn, Haydn’s own music reflected the impact of his younger friend, demonstrating his flexibility and receptivity to new ideas.1
• High Regard: Haydn held Mozart in the highest esteem. In 1785, he famously told Mozart’s father, Leopold, that he considered his son the greatest composer he had ever known, praising both his taste and his profound knowledge of composition.2

It is important to note that while Michael Haydn—Joseph’s younger brother—was also an intimate friend of Mozart, the bond between Joseph and Mozart remains a hallmark of their mature careers.13