Established: 1395 AD/CE
Disestablished: 1967 AD/CE
Kathiri (Arabic: ٱلْكَثِيْرِي, romanized: al-Kathīrī), officially the Kathiri State of Seiyun in Hadhramaut (Arabic: ٱلسَّلْطَنَة ٱلْكَثِيْرِيَّة - سَيْؤُوْن - حَضْرَمَوْت, romanized: al-Salṭanah al-Kathīrīyah - Sayʾūn - Ḥaḍramawt) was a sultanate in the Hadhramaut region of the southern Arabian Peninsula, in what is now part of Yemen and the Dhofari region of Oman.
The Kathiris once ruled much of Hadhramaut, but their power was truncated by the rival Qu'aitis in the 19th and 20th centuries, losing Al-Mukalla in the late 19th century process. The Kathiris were eventually restricted to a small inland portion of Hadhramaut with their capital at Seiyun (Say'un).
The sultanate entered into treaty relations with the British in 1888 and became a part of the Aden Protectorate. in 1916, a division occurred in Kathiri and the Sultanate of Tarim separated from Kathiri.
The Kathiri State declined to join the Federation of South Arabia, but remained under British protection as part of the Protectorate of South Arabia. Al-Husayn ibn Ali, Kathiri sultan since 1949, was overthrown in October 1967, and the following month the former sultanate became part of newly independent South Yemen.
South Yemen united with North Yemen in 1990 to become the Republic of Yemen, but local sheikhs in Yemen are reported to still wield large de facto authority.
The first Prime Minister in the history of East Timor, Mar'ī al-Kathīrī, is a third generation descendant of immigrants from Kathiri, part of a significant migration of Hadhramis to Southeast Asia in the 19th and 20th centuries. This is reflected in his name 'Alkatiri'. The Indonesian human rights activist Munir Said Thalib is also a descendant of immigrants from the Kathiris.