According to The New Penguin Dictionary of Music, Reinhard Keiser was a German composer, also director of the Hamburg Opera and afterwards for some time in Copenhagen. Wrote more than 100 operas, some with mixed German and Italian words; more than anyone else, established Hamburg as an opera centre. Also compose oratorios, a "St Mark Passion", etc.
Reinhard Keiser has a Menuett published in Leichte Trios - Easy Trios. Books: [§]Die Opern Reinhard Keisers : Studien zur Chronologie, Überlieferung u. Stilentw. by Klaus Zelm [§]Reinhard Keiser : LA Forza Della Virtu (Friedrich Christian Bressard) by Reinhard Keiser