Who is the Last Imam? When is he to come? Is this in the Qur'an? Where does this belief come from?

There are several sects in Islam. Last Imam of which sect? As far as Imamiyah or Shiah Ithna Asghari sect is concerned yhr last Imam they are waiting for is Imam Mahdi who, it is expected may reappear any time at the time of maghrib (evening) prayer.
And as far as Ismaili Tayyibi sect is concerned last Imam known is Imam Tayyib. But unlike Ithna Asharis Ismaili Tayyabi sect does not believe that Imam Tayyib will reappear but an imam from his progeny. No onje knows when he will appear but they are all in waiting.
Asghar Ali Engineer