Reinhard Keiser (9 January 1674 – 12 September 1739) was a German opera composer based in Hamburg. He wrote over a hundred operas. Johann Adolf Scheibe (writing in 1745) considered him an equal to Johann Kuhnau, George Frideric Handel and Georg Philipp Telemann (also associated with the Oper am Gänsemarkt), but his work was largely forgotten for many decades.