What is a brief overview of the Rightly Guided Caliphs?

The four Rightly Guided Caliphs are: Abu Bakr Al-Siddiq, Umar ibn Al-Khattab, Uthman ibn Affan, and Ali ibn Abi Talib. All of them were given glad tidings of Paradise, and the Prophet, peace and blessings be upon him, commanded following their Sunnah.

1. Abu Bakr Al-Siddiq: The first of the Caliphs, the first man to believe in the Messenger, and his companion during the Hijrah (migration). He was named Al-Siddiq (the Truthful) due to his truthfulness to the Prophet. He fought against the apostates and compiled the Qur'an. He passed away after two years, three and a half months of his caliphate.

2. Umar ibn Al-Khattab: The second Caliph, the Prophet nicknamed him Al-Faruq (the Discerner). He embraced Islam five years before the Hijrah. He initiated the Islamic calendar (Hijri calendar) and established the governmental departments (Diwans). During his reign, Syria, Iraq, Egypt, and Jerusalem were conquered. He was assassinated by Abu Lu'lu'ah Al-Majusi and was buried next to Abu Bakr. His caliphate lasted ten years and six months.

3. Uthman ibn Affan: The third Caliph, one of the ten who were given glad tidings of Paradise. He equipped the Army of Hardship (Jaysh Al-Usrah). During his reign, Armenia, Azerbaijan, and Africa were conquered. He compiled the Qur'an into a single Mushaf (codex). He was assassinated after being besieged in his home, and his caliphate lasted 12 years.

4. Ali ibn Abi Talib: The fourth Caliph, the Prophet's cousin and son-in-law. He witnessed all of the Prophet's battles except for Tabuk. He was pledged allegiance to the caliphate after Uthman's assassination. During his reign, major tribulations occurred, such as the Battle of the Camel, Siffin, and Nahrawan. He was assassinated by Abdur-Rahman ibn Muljam, and he was 63 years old.