The country is
Sudan. It was known as
the Sudan in colonial times. There are several countries that had the article attached to their name in the past but which no longer do.
The official name is
Sudan. The article was dropped when it became independent. The same is true of Ukraine, which was known as "the Ukraine" when it was part of the USSR. You can see the official names in the United Nations website, in the section of Member States.
المصدر
http://www.longmansec.com.eg/QuestAns.aspx?QA_ID=753
http://www.longmansec.com.eg/QuestAns.aspx?QA_ID=347