Instrumental virtuosos of the late eighteenth-century were expected to have an instinctive command of certain skills, especially the ability to improvise on a moment's notice. Although we know him primarily as a composer, Beethoven's early career saw him in the ranks of the very best performers of his time, and his command of improvisation was legendary. In all, Beethoven composed over twenty sets of piano variations. These served two purposes: they showed off his performing skills; and they helped him explore what could be done with the very essence of a theme. These exercises honed the composer's skills in thematic development, which bore fruit in his later large-scale works, many of which feature entire movements in variation form.