John the Baptist appears in two stories in Mark. In one story, he is baptizing all of Judaea when Jesus appears and he baptizes him. In another story, he is beheaded by Herod Antipas.
John the Baptizer appears in a section of Josephus’ Wars of the Jews, where the misfortune of Herod Antipas was explained as retribution for Herod killing John (the Baptizer), who was widely loved and highly respected. Compare to the historical account of Herod the Great (Antipas’ grandfather) killing John Hyrcanus II, who was widely loved and highly respected and was also a Hasmonian ethnarc of the Jews who had the favor of Rome.