I think there will be two, one false messiah and one false Elijah, aka the Sea Beast and the Earth Beast. From what I know, Jews have been expecting a reincarnation of Elijah. You remember at the beginning of the gospel of John, Pharisees sent some men to ask about the identity of John the Baptist, and they asked if he was Elijah. Till this day there's still a tradition in many Jewish families to leave an empty chair at the dinner table for Elijah. But behold, when this fella comes, he's gonna be a reincarnation of Judas, not Elijah, and he'll sell all of us out to the false messiah. That's the real Man of Sin/the Lawless One in 2 Thess. 2:3.