Hazrat Abu Bakr aka Abdullah ibn Abi Quhafa (573-634) was a close personal friend, advisor and father-in-law of the prophet Muhammad. Following Muhammad's death, Abu Bakr became the first Caliph of the Muslim empire of the Rashidun Caliphate. Known by the nickname of "Al-Siddiq" ("The Truthful"), he also became the first free man to accept the Muslim religion. Abu Bakr famously hid in a cave with Muhammad in Jabal Thawr while they were being pursued by the Quraysh. Abu Bakr provided the money and land for the first mosque constructed by Muhammad in Medina. Abu Bakr was also one of Muhammad's closest military advisors, and he participated in many battles, often as an army commander. During his short reign as Caliphate, he put down an Arab rebellion (The Ridda Wars) and successfully invaded the Byzantine and Sassanid (Persian) Empires.