Ualgarg Mór Ó Ruairc (died 1346) was King of West Breifne from 1316 until his death in 1346.
 His long and influential reign ensured that his descendants would rule West Breifne for the rest of its history, 250 years after his death.
 The rival branches of the O'Rourke sept which emerged in the 15th century - the Carrigallen O'Rourkes, Dromahair O'Rourkes and Carha O'Rourkes - all trace the lineage back to Ualgarg Mór.
O'Connor (Middle Irish: Ó Conċuḃair; Modern Irish: Ó Conċúir), is an Irish Gaelic aristocratic and landed gentry family who are the historic Kings of Connacht and the last High Kings of Ireland before the Norman invasion.
 The family seat is Clonalis House outside Castlerea in County Roscommon.
 The O'Connor family can trace their lineage back to the 5th century without dispute but through folklore and mythology to Adam.
 The clan name originated in the 10th century as a derivative of its founder Conchobar mac Taidg Mór.
 The family contributed to Irish society in art, history, language, politics, diplomacy, etc..
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 before and during colonial rule in Ireland.They descend in the paternal line from the Connachta's Uí Briúin Ai.
 The current O'Connor Don is Desmond O'Connor Don (b. 22 September 1938) who lives in Rotherfield, East Sussex in England.
Gurney is an English surname of Anglo-Norman origin.
 Some families with this surname can trace their lineage back to the Counts de Gourney, who arrived in Britain with William the Conqueror in 1066.
Harald "Bluetooth" Gormsson (Old Norse: "Haraldr Gormsson" , Danish: "Harald Blåtand Gormsen" , died c. 985/86) was a king of Denmark and Norway.
The history of Denmark as a unified kingdom began in the 8th century, but historic documents describe the geographic area and the people living there—the Danes—as early as 500 AD.
 These early documents include the writings of Jordanes and Procopius.
 With the Christianization of the Danes c. 960 AD, it is clear that there existed a kingship in Scandinavia, controlling the current Danish territory roughly speaking.
 Queen Margrethe II can trace her lineage back to the Viking kings Gorm the Old and Harald Bluetooth from this time, thus making the Monarchy of Denmark the oldest in Europe.
 The area now known as Denmark has a rich prehistory, having been populated by several prehistoric cultures and people for about 12,000 years, since the end of the last ice age.
Zubayd or Zubaid is a large Arab tribe that migrated to Iraq, before and after the Islamic conquest.
 The tribe was an offshoot of the Yemeni tribe of Madhhij, which is a majority Qahtanite Arab tribe.
 However, a few branches of the tribe such as the al-Bu Hamid, al-Bu Yusef and al-Bu Ali sects trace their lineage back to Adnan through Elias ibn Mudhar and so are Adnanite Arabs, recognised as Zubayds only by early settlement and migration.
 The Zubayd tribe hails from and derives its name from a town on Yemen's western coastal plain known as Zabid.
 Its first leader was the companion of Mohammed, named Amru bin Ma'adi Yakrib .
The 5th Light Infantry was an infantry regiment of the Bengal Army and later of the "raj"-period British Indian Army.
 It could trace its lineage back to 1803, when it was raised as the 2nd Battalion, 21st Bengal Native Infantry.
 The regiment was known by a number of different names: the 42nd Bengal Native Infantry 1824–1842, the 42nd Bengal Native (Light) Infantry 1842–1861, the 5th Bengal Native (Light) Infantry 1861–1885 and the 5th Bengal (Light) Infantry 1885–1903.
 Its final designation 5th Light Infantry was a result of the Kitchener Reforms of the Indian Army, when all the old presidency titles (Bengal) were removed.
 During World War I the regiment was stationed in Singapore and was notorious for its involvement in the 1915 Singapore Mutiny.
 The regiment was disbanded in 1922, after another set of reforms of the post World War I Indian Army.
The Sippenbuch was a genealogical clan book carried by every member of the SS.
 This measure was imposed by SS leader Heinrich Himmler to ensure the racial purity of the SS, who he described as a 'racial upper strata of a Germanic people'.
 Under the "Sippenbuch" regulations, each member of the SS had to be able to trace their lineage back to 1750 to prove they were of 'Aryan' descent.
 Prospective marriage partners were required to provide the same evidence about their ancestry.
The 31st Battalion, Royal Queensland Regiment (31 RQR) was a Reserve infantry battalion of the Australian Army.
 Although it was officially formed as 31 RQR in 1965 the battalion can trace its lineage back to units formed in 1881 as part of the colonial defence forces of the state of Queensland.
Ayatollah Haydar al-Sadr (Arabic: أية الله حيدر الصدر‎ ‎ ) (1891–1937) was born in Samarra, Iraq.
 His father, Ismail as-Sadr (d. 1920) was a Grand Ayatollah and the first to be use the as-Sadr surname, which came to be associated with a long line of religious scholarship within Shia Islam.
 Haydar and the as-Sadr family are also considered as Sayyid, or those who can trace their lineage back to Muhammad (d. 632).
 The family's lineage is traced through Imam Jafar al-Sadiq and his son Imam Musa al-Kazim the sixth and seventh Shia Imams respectively.
 This direct and meticulously documented lineage is unprecedented even among the illustrious families in the Islamic world who claim such lineage.
 The Shia Muslims consider themselves the followers of Muhammad's bloodline, thus a great deal of respect and reverence is paid to the "Sayyids" throughout society.
 Some of the well known relatives of Haydar al-Sadr include his brother, Sadr al-Din Sadr (d. 1954), his nephew Moussa as-Sadr and another nephew Mohammad Sadeq al-Sadr.

Question: Who can trace their lineage back to a king of Denmark and Norway that died in 985/86?
Answer: Queen Margrethe II