The Rightly-Guided Khalifas
When the Prophet MuhammedSAW died (632 C.E.), Hadhrat Abu Bakr succeeded to his spiritual, political, and administrative functions as successor of the messenger of God (khalifa rasul Allah). Bernard Lewis, the preeminent historian of Islam, observes:
“Abu Bakr was given the title of Khalifa or ‘Deputy’ (of the prophet) … and his election marks the inauguration of the great historic institution of the Caliphate. His electors can have no idea of later functions and development of the office. At the time, they made no attempt to delimit his duties or powers. The sole condition of his appointment was the maintenance of the heritage of the Prophet.” 
Bernard Lewis captured the essence of the institution of khilafat in the last sentence by re-stating the phrase “on the precept of prophethood” from the hadith. The first four Khalifas, Abu Bakr, Umar, Uthman, and Ali, were close associates of the Prophet known for their high integrity and great devotion. The qualificationrightly-guided (the rashedun) has been historically applied to them to distinguish them from the kings-caliphs who followed them.
The period of the reign (632-661) the rightly-guided Khalifas constituted what later generations of Muslims would often remember as a golden age of pure Islam. Muslims would often define themselves and their theology according to the way they assessed the glorious, though turbulent and short-lived, events of that formative period .
The famous historian of Islam, Muhammad ibn Jarir Al Tabari, relates the following incident .
“Umar said to Salman: ‘Am I a king or a khalifa?’ and Salman answered: ‘If you have levied from the lands of the Muslims one dirham, or more, or less, and applied it unlawfully, you are a king not a khalifa’. And Umar wept.” [Al Tabari, Tarikh al-Rusul Wal Muluk]
Here Hadhrat Umar, the second Khalifa, whose piety, sense of justice, and puritanical austerity were proverbial, came to tears by the mere mention of the possibility of misusing a single coin from the public exchequer. This incidence underscores the distinctive characteristics of the rightly-guided khilafat.
The rightly-guided Khalifas played active spiritual and secular roles. They were the head of the Islamic confederation and exercised secular authority often indirectly through appointed governors of various provinces of the empire.
After the assassination of Hadhrat Ali (661 C.E.), the last of the rightly-guided Khalifas, the question of the right to khilafat resulted in a major split in Islam into Sunni and Shia branches . Muawiyah declared himself the khalifa of the ummah and of the Muslim empire and thereby laid down the foundations of a long line of dynastic monarchy – quite in accordance with the prognostications made by the Prophet.