John the Baptist (known as the prophet Yahya in the Quran), also known as John the Baptizer, was a Jewish itinerant preacher in the early first century AD. John is revered as a major religious figure in Christianity, Islam, the Bahá'í Faith, and Mandaeism. He is called a prophet by all of these traditions, and is honoured as a saint in many Christian traditions.

John used baptism as the central symbol or sacrament of his messianic movement. Most scholars agree that John baptized Jesus. Scholars generally believe Jesus was a follower or disciple of John and several New Testament accounts report that some of Jesus' early followers had previously been followers of John. John the Baptist is also mentioned by the Jewish historian Josephus. Some scholars maintain that John was influenced by the semi-ascetic Essenes, who expected an apocalypse and practiced rituals corresponding strongly with baptism, although no direct evidence substantiates this.

According to the New Testament, John anticipated a messianic figure greater than himself. Christians commonly refer to John as the precursor or forerunner of Jesus, since John announces Jesus' coming. John is also identified with the prophet Elijah.