Jesus warned his followers not to be deceived by false messiahs. Many people would come claiming, ‘I am He,’ and would lead many others astray. These people claimed either to be the long-awaited Jewish Messiah or to speak with the Messiah’s authority.
Some examples include
Theudas the Galilean (Acts 5:36),
Simon, the son of Gioras, and
John of Gischala, who tricked many people in the AD 60s.