In Iraq I have heard of a group calling themselves the Mahdi's Army. They do not, as far as I am aware, represent the idea or prophecy of the Imam Mahdi as believed by my friends. But like so much that is beautiful and good in Islam, we are not able to control people from using names and symbols of our religion and spirituality. And sometimes, mad people use them for bad reasons. Let's face it, things are an absolute mess now in Iraq (still).
The lore of the Imam Mahdi is growing. Perhaps one day, if I live long enough, I might share with you whatever that I am informed.
God bless the 2nd Coming of Jesus, and God bless the Coming of the Mahdi! They shall come from the Cruxible of Love and Divine Power, and their Mercy, Justice and Compassion shall surprise and awe the followers of all religion, including Islam and Christianity. Especially Islam and Christianity,