The truth about the Mahdi, and the order in which the portents of the Hour will appear


In the present distressed situation many people including scholars are found to talk about the Renaissance of Islam and the emergence of Imam Mehdi. I want to ask about two things: first, who is or may be Imam Mehdi and is there any evidence about his possible emergence, in the light of Quran and Hadith. Secondly what will be the order of occurence of events before the Qiyamat, including emergence of Imam Mehdi, Fitna-e-Dajjal, Yajooj Majooj and Hazrat Issa (Jesus). Kindly reply in detail.