Khalifah
From Muftipedia
Khalifah is an Arabic word meaning the Islamic leader of the Ummah. Most Commonly used for the successors of the Prophet Muhammed (peace be upon him).
The four famous khalifa's are known as 'Khulafaa-e-Rashideen'. They are as follows;
1. Abu Bakr (ra) 11 Ah - 13 AH
2. Umar (ra) 13 AH - 24 AH
3. Uthman (ra) 24 AH - 35 AH
4. Ali (ra) 35 AH - 40 AH