Abu Bakr became the Prophet’s companion in His Migration to Madina. After the migration Abu Bakr took part in all activities with the Prophet; he fought with the Prophet in the battle of Badr, Uhud and Khandaq. The Prophet consulted him about all problems and generally accepted his opinions. Abu Bakr was elected as the caliph after death of the Prophet. He fought against rebels who abjured Islam. After he defeated the rebels he organized military campaigns to conquer the territory of Byzantium and Persians (Sasanids). Abu Bakr reigned for two years as caliph. Before his death, he assigned Omar as the second caliph