Which Caliph (Khaleefa-e-Rashid) died a natural death?

Abu Bakr is the only Rashidun Caliph who died of natural causes. He died of illness after reigning for two years, two months, and 14 days. Abu Bakr is buried in the Green Dome at the Al-Masjid an-Nabawi in Medina, the second holiest site in Islam.
Abu Bakr was Muhammad's father-in-law and succeeded him to political and administrative functions.