Imam, Sheik, Mullah

Factual Questions
1

What are the (different) meanings of these terms?

I had thought that a sheik was a political rather than religious leader, but Sheik Omar Abdul Rachman (of WTC fame) was aparently the latter - unless he just happened to have occupied the former position as well. So when I hear, for example, that the British have turned over some administration of Basra to a “local sheik”, I am unclear if that refers to a religious or political figure. (If the latter, how does one become a sheik? Is it inherited?)

As for Mullah, I seem to have seen it primarily (or perhaps exclusively) with regards to Taliban leaders - perhaps it is unique to them?

In sum, fill me in - which groups use which titles and exactly what do they represent. And if there are any other similar titles, feel free to describe those as well.

Thanks!

2

Here’s a primer: http://slate.msn.com/id/1008399/

The only major ones this page misses are “Hajji” (one who has gone on the Hajj) and Mahdi.

Mahdi is very complex and the meaning varies especially between Sunni and Shia. For the Shia, the Mahdi is an eschatological figure who will lead the faithful to kill all who live in Dar-al-Harb.

For Sunni, there can be several mahdis, since the term therein refers to one who is led by God. Thus, converts might be addressed as “mahdi”, since it would be held that God led them to Islam.