Today, the Hashemites are best known as the rulers of Jordan. They had ruled the Arabian Peninsula until they were driven out by the more religiously austere Wahhabi-backed Saud family with the fall of the Ottoman Empire. In April 1921, Abdullah ibn Hussayn negotiated with then-colonial secretary Winston Churchill to be the administrator of British-occupied Trans-Jordan (present-day Jordan), thus removing Trans-Jordan from the implications of the Balfour Declaration.
Abdullah named himself king and built Jordan into the modern nation-state it is today. Britain installed another Hashemite, King Faisal, king of Iraq (1921-1933) after a brief stint as king of Syria.
The Hashemites have had a checkered, violent history--losing the Arab Peninsula, losing Syria and Iraq, and under King Hussein, losing East Jerusalem in the 1967 Six Day War. Today, Jordan is ruled by King Abdullah II, who succeeded Kinh Hussein in 1999, when Hussein--a chain-smoker--died of cancer.
The Hashemites, Robert Fisk writes in The Great War for Civilization, have "always lived on the edge, provoking disaster and recovery with a drama and nerve that still astonish other Arab leaders. They have a tendency to move rapidly between rage and contemplation, political folly and eternal friendship, that might be characteristic of the Gulf Arabs rather than the Levant."