How many caliphs ruled after Muhammad died?

After Muhammad's death in 632 CE, there were four main caliphs known as the "Rightly Guided Caliphs." They were Abu Bakr, Umar, Uthman, and Ali. Following these four, the Umayyad and Abbasid caliphates emerged, leading to a long line of caliphs in Islamic history. However, the initial period is primarily defined by these four caliphs.