The Shiite rebels who seized Yemen's capital of Sanaa, known as the Houthis, are followers of the Zaydi branch of Shiite Islam. Here is a look on who the Zaydis are:

— Zaydis are a small branch of Shiite Islam, and the community is almost entirely located in Yemen. It is distinct from the "Twelvers," Shiite Islam's largest branch, predominant in Lebanon, Iraq and Iran. Zaydis are estimated to make up at least 30 percent of Yemen's population of nearly 30 million people, and around 8 percent of the 70 million Shiites around the world.

— Zaydi is considered to be the closest Shiite branch in doctrine to Sunni Islam. It is named after Zayd, the great-grandson of Imam Ali, whose descendants Shiites believe were the true leaders of Islam, or "imams," after the Prophet Muhammad.

Twelver Shiites, for example, trace a line of 12 imams, including Ali and his descendants. They believe the 12th imam vanished and one day will return as the messiah-like figure the Mahdi. Zaydis reject this doctrine and believe that anyone descending from the house of Ali is eligible for the Imamate.

— The closeness of Zaydism to Sunni Islam is one reason sectarian differences in modern Yemen have rarely been strong. Zaydis are deeply integrated into the country's power structure, military and government. Former President Ali Abdullah Saleh, for example, was a Zaydi, but during his rule he often struck alliances with Sunni conservatives and he fought the Houthi rebels.

— The Zaydis founded a dynasty known as the imamate in northern Yemen that ruled for some 1,000 years. A 1962 revolution in Yemen toppled the last imam, Mohammed Ahmed, and established a republic. The imamate has been vacant since. The Houthi rebels say they have no intention of restoring the imamate, but are rather working for a democratic and inclusive Yemen.

— The Houthis are named after the Houthi family from the northern Yemeni region of Saada which claims descent from the Prophet Muhammad. But not all Zaydis support them. The highest Zaydi religious authorities have so far kept silent on the latest events. The Houthis lost a young and innovative religious scholar when their leader Hussein al-Houthi was killed in 2004. They are now led by 33-year-old Abdul-Malik al-Houthi.