The Hashemites or the Bani Hashim are the direct descendents of the Prophet Muhammad (peace be upon him), through his daughter Sayedatna Fatima and (her husband) his cousin Sayedna Ali (the fourth, and last, "Rightly-Guided" Caliph of Islam). "Hashim" was the name of the great-grandfather of both the Prophet Muhammad (pbuh) and the Caliph Ali. The Hashemite family ruled, in various forms, over the Hejaz (the Western part of Arabia which includes the Holy cities of Mecca and Medina) from the time of the Caliph Ali in the Seventh Century CE until 1925 CE.
On June 10th, 1916, Sherif Hussein Ibn Ali declared the Great Arab Revolt to liberate land and man, establish an independent Arab state, and put the Arabs in a worthy position, in a turbulent world, at a time where wars were waged for economic and political interests, as well as for nationalism and independence. The Great Arab Revolt led to distinct Hashemite Kingdoms for the sons of Sharif Hussein of Mecca in Transjordan, Syria, Iraq and the Hejaz, but the only one to survive to this day is that of Transjordan, which since 1946 has been renamed the Hashemite Kingdom of Jordan.
The four kings of Jordan have been: (1) King Abdullah I (the son of Grand Sharif Hussein of Mecca; the founder of modern Jordan in 1921, and, thereafter, its ruler from (1921-1951); (2) his son King Talal (r. 1951-1952); in this short time King Talal established the National Constitution of Jordan); (3) King Talal's son, the late King Hussein (r. 1952-1999), the great builder of modern Jordan; and (4) King Hussein's eldest son, King Abdullah II the 41st generation direct descendant of the Prophet Muhammad (Peace Be Upon Him) (r. 1999- present day).