This is the Farnese Bull, widely believed to be the largest recovered statue from antiquity. It's not in Pompeii, but the National Archeological Museum in Naples (which contains the recovered artifacts from Pompeii) and is Greek in origin. It relays the myth of Dirce in which the sons of Antiope tied Dirce to the wild bull as punishment for disrespecting their mother. It has been restored numerous times, most famously by Michelangelo.