Well here's one I hadn't heard before. In his biography of the emperor Constantine the Great, Ramsay MacMullen tells us that as a young man Constantine's nickname was "bullneck":
It is said that [Constantine's] being sent to Diocletian's court was partly for the purpose of educating him, but there is more evidence of his physical growth than of his mental. He attained an average height but a very robust build and great strength. His fellows treated him with respect and nicknamed him Bullneck.