What was Oppenheimer's first name?

More than 100 years after he was born, we’re still not quite sure.

By Brye Steeves | February 16, 2021

Oppenheimers Name Opt
Oppenheimer visits with Dorothy McKibbin (left) and another friend. CREDIT: Los Alamos National Laboratory

Physicist J. Robert Oppenheimer is known as the father of the atomic bomb. However, 117 years after his birth on April 22, 1904, his first name—what the letter J may or may not stand for—is still a mystery.

By far, most sources—including Oppenheimer’s own birth certificate—state that Oppenheimer’s first name was Julius. According to the Pulitzer Prize–winning biography American Prometheus, Oppenheimer was named after his father, a Jewish textile importer. This could be considered unusual, however, because naming a baby after a living relative is contrary to European Jewish tradition.

"I have no first name other than the letter J, and that my full and correct name is J Robert Oppenheimer.”- J. Robert Oppenheimer

Forty years later, a letter from the War Department that granted Oppenheimer his security clearance states “Julius” as his first name.

Numerous other people, though—including Oppenheimer himself— insisted the J didn’t stand for anything at all. In a 1946 letter to the U.S. Patent Office, Oppenheimer wrote: “This is to certify that I have no first name other than the letter J, and that my full and correct name is J Robert Oppenheimer.”

Oppenheimer’s obituary, which was published in The New York Times a day after he died at the age of 62 from throat cancer, explains that “J. (for nothing) Robert Oppenheimer lived the remainder of his life [after the 1945 Trinity test] in the blinding light and the crepusculine [sic] shadow of the world’s first manmade atomic explosion, an event for which he was largely responsible.”

Regardless of whether he was Julius or just the letter J, many called him by the nickname he earned in his mid-20s that stuck for the rest of his life: Oppie. (Though it may be Oppy or Opje.)