Zaidi's are originally descendants of the Prophet Muhammed (as), who used to reside in what is now currently modern day Saudi Arabia. The Zaidi family name begins with the son of Imam Zain-Al-Abideen (as) - He was the Prophet Muhammed's great-grandson. The son's name was Zaid. And thus all those who can trace their lineage through Zaid are known as Zaidis. Like most Arabs during that era, the Zaidis lived in a tribal structure. This tribe ended up moving from Arabia to the regions of modern day Iran and Iraq. From there the Zaidi tribe settled in many parts of the Middle East and the Indian Subcontinent.