Margarete Ulrike Augusta Marie Karoline Elsa Reger (née von Bagenski; previously von Bercken, 25 October 1870 – 3 May 1951) was a German writer, the wife of the pianist and composer Max Reger, whose memory she kept alive by founding an archive, the Max-Reger-Institute, and a foundation, all dedicated to him and his work.

[2] She met Max Reger in 1893, when she spent a summer vacation in Wiesbaden, where she took voice lessons with him.

[3] They married on 7 December 1902 in Bad Boll and lived in Munich.

Elsa followed the composer, whose fame increased, to Leipzig, Meiningen and Jena.

[1][5] After her husband's death in 1916, she took care of their daughters and also kept his memory alive.