H.J. Eysenck, one of the two most important HBD researchers (the other being Arthur Jensen, also part Jewish) was half Jewish, a fact he hid for most of his life, according to this article.

We have proved beyond doubt that Eysenck was in fact half Jewish on his mother’s side, and therefore strictly Jewish according to Rabbinic law (Halacha). Using techniques and resources of Jewish genealogy, we discovered that his maternal grandmother’s birth name was Helene Caro. We then located her marriage certificate, which confirmed that both Helene and her husband (Eysenck’s maternal grandfather) Max Werner belonged to long-established Jewish families.

Without the contributions of Jews, HBD probably wouldn’t even exist. It was from reading the books and articles of Arthur Jensen and H.J. Eysenck at the Van Pelt Library at the University of Pennsylvania that I learned about the science of HBD (which at the time was not called HBD, that term was coined by Steve Sailer).