Hisham ibn Abd al-Malik
About the question of whether Baqir was known by this name, during his life or after that, there is narration in which, the Caliph, Hisham ibn Abd al-Malik, asks Zayd, Baqir's half brother, about his brother al-baqara (the cow) implying al-baqir. Zaid answers Caliph by saying that the prophet Muhammad, called his brother al-baqir (he who splits open knowledge)