Brother Nabiel teh version of Imam mehdi u are talking about is the SHIA version.
They believe that Imam mehdi RAN AWAY , and he took with him a lot of stuff that the ummah could have used , Like the ORIGINAL QURAN ( claiming the one we have is not complete) HE TOOK WITH HIM THE STICK OF MOSES Alihi as sallam lol All sort of non sense , how can a sane person ever believe them.
Basically they say he ran away and he will come back , so lol he has been alive for about a thousand year , may be he is just hybernating or something.
But very clear Authentic ahadeeth do not say that , He will be a person Who Allah will guide , His name wont be mehdi , so dont anme ur kids mehdi hoping they will become mahdi , His name will be Muhamad Ibn Abdullah , Like the prophet sala lahu lihi wa salam told us that The mahdi's name will be similar to My Name and his Fathers name will be similar to my Fathers Name.
Get the facts , The wiki info seems to be the shia version of mahdi , They also have lots of crazy ideas about the mahdi , Khomeini claims in his book that he is the deputy mahdi and now mahdi will come soon and from amaong the things mahdi will do is he will dig the grave of abu baakr radi Allahu Anhu n Umer Radi Alahu Anhu and hang their bodies on a tree and burn them , ASTAGHFIRULLAH! and also that he will Dig out the Body of Aishah Radi Alahu Anha n punish her with lashes , the punishment of zina , ASTAGHFIRULLAH!!
IS THIS MAHDI OR DAJJAL . THE MEHDI THAT SHIA ARE WAITING FOR CAN ONLY BE A DAJJAL , n yeah He also claism that They will take the Black stone from the kaaba n place it in Koofa!!! Yes that mahdi for u
But as far as the Mahdi The Prophet sala lahu alihiwa sallam informed us about then he is free from all this non sense n this CRAP !!!
Check this brief talk by our brother Abu Uwais Rahimahullah , Its in english he was an american brother its not long , about 7 minutes
http://www.youtube.com/watch?v=9ufyKEFsE0M