There are a number of examples of false Messiahs throughout the generations - men who have claimed to be the Messiah when they weren't. In 6 A.D. Judas of Galilee led a rebellion against the Romans, and then claimed to be a Messiah. Attempts were frequent during Roman times, but most of these men were captured by the Romans and duly executed.

The leader of the Bar Kochba revolution, Simon Ben Kochba, was believed to be the Messiah by Rabbi Akiva. In response, Simon claimed to be a, not the, Messiah. However, in the revolution, hundreds of thousands of Jews died as the Romans eventually put it down. This was not the work of the Messiah.

The need for a Messiah figure is obviously great, and hence in times of persecution, one can expect more people to claim to be THE leader and who will try to help their people out. Others are simply dellusional, such as the one who tried to convert Pope Nicholas III, with whom he obtained an audience! Not surprisingly, he was burned at the stake.

There have also been people (usually men, although Eve Frank claimed to by "the Holy Lady") who have claimed to be ELijah, the prophet who brings in the Messiah.

Whatever, many people assume that many others are the Messiah, but never ask them for signs or anything of the sort. The Messiah will not need to be tested, he will reveal himself at the right time. That is why there are so many false Messiahs - because those that do attempt to prove their 'powers' usually end up dying because of them, hence proving them to be truly somebody very human.