What were Abu Bakr's greatest achievements?

Abu Bakr aka Abdullah ibn Abi Quhafa (573-634) was the Prophet's (saw) closest friend. His achievements included: He was the first free man to unhesitatingly believe the Messenger (saw) in Mecca achieving the title of al-Siddiq, He built the first mosque in Islam in the courtyard of his home, He freed eight slaves including four men: Bilal ibn Ribah, Abu Fakih, Ammar ibn Yasir and Abu Fuhayra and four women: Lubaynah, Al-Nahdiah, Umm Ubays and Harithah bint al-Muammil He was the Prophet's closest advisor and father-in-law, He alone accompanied the Messenger during hijra famously hiding in a cave in Jabal Thawr while pursued by Quraysh, He along with Umar Ibn al-Khattab were the only two viziers in Medina, Abu Bakr provided the money and land for the first mosque constructed by the Prophet (saw) in Medina, Abu Bakr was also one of Muhammad's closest military advisors, and he participated in many battles, often as an army commander, He was told he was amongst ten companions guaranteed paradise, He led the prayers when the Prophet (saw) was on his deathbed, Following the Prophet's (saw) death, Abu Bakr became the first Caliph of the growing Rashidun Caliphate empire, He compiled the first copy of the Qur'an, He put down many rebellions by Arab tribes (the Ridda Wars) and successfully invaded the Byzantine and Sassanid (Persian) Empires, and He recommended Uthman bin Affan to be the next caliph whilst on his deathbed.

1. He was known as Al-Siddiq or the truthful one; 2. Hazrat Abu Bakr had been a close companion of Prophet Muhammad (saw) and was elected as the first khalifah of Islam in 632 CE; and 3. He dealt with tribal rebellions amongst the Arabs and unified them, spreading Islam to Syria in the process.