Mark 13:5

And Jesus began to say unto them, Take heed that no man lead you astray. Many shall come in my name, saying, I am he; and shall lead many astray.

Although primarily addressed to the apostles, there are nevertheless overtones in this extending to eternity.

Many shall come in my name ... Matthew quoted Christ as saying that these impostors shall claim to be the Christ. Bickersteth said, "Such (false christs) were Theudas (Acts 5:36) and Simon Magus (Acts 8:10)."[19] The latter, according to Jerome, claimed to be Almighty God in the flesh, clearly an example of a false Christ. The apostles were admonished not to be led astray by such claims; and the admonition is binding upon Christians of all generations who are continually tempted by all kinds of impostors and charlatans pretending divine honors.

I am he ... There is a variation in Mark's record that should be noted. The Greek text omits "he," evidently supplied by the translators with respect to Matthew's account. However, it is not necessary to "reconcile" the two by any such device, for the Lord made both statements. Mark's quotation of the Lord refers to impostors claiming to be "God," that being the meaning of "I AM," as in Exodus 3:6,14; Matthew 22:32; John 8:58, etc. The current era has had several such.