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Masih ad-Dajjal (Arabic: الدّجّال, literally "The Impostor"), is an evil figure in Islamic eschatology. He is to appear pretending to be Allah at a time in the future, before Yawm al-Qiyamah (The Day of Resurrection, Judgment Day). It is said that he will have one eye damaged and the other will be working. Dajjal is a common Arabic word, used in the sense of "false prophet", but al-Masih ad-Dajjal, with the definite article, refers to "the impostor", a specific end-of times deceiver. The term al-Masīḥ ad-Dajjāl (Arabic for "the false messiah") is a literal translation of the Syriac term Mšīḥā Daggālā, which had been in the common vocabulary of the Middle East and adapted into the Arabic language 400 years prior to the Qur'an via the Peshitta (which uses that term instead of the Greek "Antichristos"). The belief is based around the events prior to the Day of Judgment around the Second Coming of The Christ, when ad-Dajjal who is blind in his right eye, shall gather an army of those he has deceived and lead them in a war against Imam Mahdi, who shall be accompanied by an army of the righteous.
He will appear somewhere between Syria and Iraq, at which time Jesus will return and he will defeat ad-Dajjal in Palestine. Ad-Dajjal will travel the whole world in forty days preaching his falsehood but will be unable to enter Makkah or Madinah.
Muhammad had given many signs of the appearance of the Dajjal and exhorted his followers to recite the first and the last ten verses of Sura Al-Kahf, as protection from the trials and mischief of the Dajjal. The Qur'an doesn't mention the Dajjal by name, like the Hadith. A couple of hadith describe the Dajjal as follows:
The Prophet mentioned the Massiah Ad-Dajjal in front of the people saying, Allah is not one eyed while Messiah, Ad-Dajjal is blind in the right eye and his eye looks like a bulging out grape. While sleeping near the Ka'ba last night, I saw in my dream a man of brown color the best one can see amongst brown color and his hair was long that it fell between his shoulders. His hair was lank and water was dribbling from his head and he was placing his hands on the shoulders of two men while circumambulating the Ka'ba. I asked, 'Who is this?' They replied, 'This is Jesus, son of Mary.' Behind him I saw a man who had very curly hair and was blind in the right eye, resembling Ibn Qatan (i.e. an infidel) in appearance. He was placing his hands on the shoulders of a person while performing Tawaf around the Ka'ba. I asked, 'Who is this? 'They replied, 'The Masih, Ad-Dajjal.' "
Once Allah's Apostle stood amongst the people, glorified and praised Allah as He deserved and then mentioned the Dajjal saying, "l warn you against him (i.e. the Dajjal) and there was no prophet but warned his nation against him. No doubt, Noah warned his nation against him but I tell you about him something of which no prophet told his nation before me. You should know that he is one-eyed, and Allah is not one-eyed."
Allah's Apostle said, "Shall I not tell you about the Dajjal a story of which no prophet told his nation? The Dajjal is one-eyed and will bring with him what will resemble Hell and Paradise, and what he will call Paradise will be actually Hell; so I warn you (against him) as Noah warned his nation against him."

Article from : http://en.wikipedia.org/wiki/Dajjal