Daniel Speer (1636–1707) was a German composer, violinist, and music theorist, primarily known for his contributions to early Baroque music. He is often associated with the early development of opera and secular vocal music in Germany. Speer's genre spans sacred and secular music, with a focus on cantatas and orchestral works. Notable works include his collection of cantatas, "Musicalische Predigten" (Musical Sermons), and the opera "Der Teufel als Beelzebub," which is recognized as one of the earliest operas in the German language. His compositions often blend lyrical melodies with rich harmonies, reflecting the stylistic transitions of the time. Speer's impact on music is significant in the context of German musical development, particularly in the evolution of the cantata and operatic forms. He also contributed to music theory through his writings, influencing future generations of composers. His efforts helped lay the groundwork for the flourishing of German music in the late Baroque period, setting the stage for later figures like Johann Sebastian Bach.