Johannes Brahms's father was rumored to be of Jewish descent (see Daniel Beller-McKenna, Revisiting the Rumor of Brahms's Jewish Descent). However, we may never know the truth.
In his preface to the Foundations (xxxviii) Lord Redesdale wrote:
"Some people have thought that Brahms was a Jew, that his name was a corruption of Abrahams. But this is false. Brahms came of a Silesian family, and in the Silesian dialect Brahms means a reed. (See an interesting paper in Truth of January 13, 1909)."