In Pirkei Avos, it mentions a תנא called בן בג בג.
Why is the תנא - בן בג בג called בן בג בג?
In Pirkei Avos, it mentions a תנא called בן בג בג.
Why is the תנא - בן בג בג called בן בג בג?
Tosfos Chagiga 9B explains that he was a convert, and the gematria of bag bag is 5 and 5 representing the Heh added to Avraham and Sarah, the parents of all converts:
בר הי הי להלל. יש מפרשים שגר היה והיינו בן אברהם ושרה שנתוסף ה"א בשמן וכן בג בג דכולה הגמרא עולה ה':
I don't recall the source right now (it might have been the 'Arukh), but it is said to be an acronym (ב.ג.ב.ג.) for בן גר בן גיורת (son of male convert son of a female convert). The name was intended to protect his/his family's identity at a time under the Romans when it would have been considered to be a capital offense to convert to Judaism.