Rabbi Gedalyah Ibn Yechiyah in Shalshelet Hakabbah wrote:
"In the fourth year of the previously mentioned emperor [Trayatzo (/Trajan?)]...there was a noble priest called Eccasia [אכקזיה] and in my opinion, this is Onkelos the Convert, who greatly loved a Jewish woman in the Punic (?) city of Isula and converted and took her as his wife and translated [the Torah] into the Greek language..."
I don't know if I properly translated the text, but does anyone know who this Eccasia/אכקזיה was that the S"H identifies with Onkelos?