Mary (mother of Jesus)
The statement that Joseph "knew her not till she brought forth her first born son" (Matthew 1:25 DouayRheims) has been debated among scholars, with some saying that she did not remain a virgin and some saying that she was a perpetual virgin. Other scholars contend that the Greek word heos (i.e., until) denotes a state up to a point, but does not mean that the state ended after that point, and that Matthew 1:25 does not confirm or deny the virginity of Mary after the birth of Jesus. According to Biblical scholar Bart Ehrman the Hebrew word almah, meaning young woman of childbearing age, was translated into Greek as parthenos, which only means virgin, in Isaiah 7:14, which is commonly believed by Christians to be the prophecy of the Virgin Mary referred to in Matthew 1:23. While Matthew and Luke give differing versions of the virgin birth, John quotes the uninitiated Philip and the disbelieving Jews gathered at Galilee referring to Joseph as Jesus's father.

Q: Who do Christians believe is prophesized in Isaiah 7:14?
Virgin Mary