Question: Ivar the Boneless was the brother of which 9th century Viking chieftain?
Context: When the Viking chieftain Rollo obtained via the Treaty of Saint-Clair-sur-Epte the territories which would later make up Normandy, he distributed them as estates among his main supporters.  Among these lands were the seigneurie of Harcourt, near Brionne, and the county of Pont-Audemer, both of which Rollo granted to Bernard the Dane, ancestor of the lords ("seigneurs") of Harcourt.  The first to use Harcourt as a name, however, was Anquetil d'Harcourt at the start of the 11th century. Ímar (Old Norse: "Ívarr" ; died c. 873) was a Viking leader in Ireland and Scotland in the mid-late ninth century who founded the Uí Ímair dynasty, and whose descendants would go on to dominate the Irish Sea region for several centuries.  He was the son of the king of Lochlann, identified in the non-contemporary "Fragmentary Annals of Ireland" as Gofraid.  The "Fragmentary Annals" name Auisle and Amlaíb Conung as his brothers.  Another Viking leader, Halfdan Ragnarsson, is considered by some scholars to be another brother.  The Irish Annals title Amlaíb, Ímar and Auisle "kings of the foreigners".  Modern scholars use the title "kings of Dublin" after the Viking settlement which formed the base of their power.  Some scholars consider Ímar to be identical to Ivar the Boneless, a Viking commander of the Great Heathen Army named in contemporary English sources who also appears in the Icelandic sagas as a son of the legendary Viking Ragnar Lodbrok. The Strongbow Saga is a historical fiction series by Judson Roberts.  The Saga tells the story of Halfdan Hroriksson, a young Viking trying to avenge his brother's murder.  The series weaves the story of the fictional Halfdan into the lives of actual historical figures of the period, including famous Viking leaders Ragnar Lodbrok, Ivar the Boneless, Bjorn Ironside, and Hastein, as well as Frankish leaders King Charles the Bald and Count Robert the Strong.  Actual historical events form a backdrop for parts of the story, including a Danish attack up the Seine River in the year 845 which was reported in several contemporary Frankish sources, including the Annals of St. Bertin. Odda, also known as Oddune, was a ninth-century ealdorman of Devon.  He is known for his victory at the Battle of Cynwit in 878, where his West Saxon forces defeated a Viking army led by Ubba, brother of the Viking chiefs Ivar the Boneless and Halfdan Ragnarsson. Hastein (Icelandic: "Hásteinn") (also recorded as "Anstign", "Haesten", "Hæsten", "Hæstenn" or "Hæsting" and alias "Alsting") was a notable Viking chieftain of the late 9th century who made several raiding voyages. Berle-Kari (Berle-Kåre; Old Norse: "Berðlu-Kári" ) was a viking chieftain who lived in ninth-century Norway.  His home was at Berle (Old Norse: "Berðla"), in present-day Bremanger in Sogn og Fjordane county. " Landnámabók" names him as the son of Vemund, and brother of Skjoldolf, one of the early settlers of Iceland. Ubba, also known as Hubba, Ubbe, and Ubbi, was a mid-ninth-century Viking chieftain and one of the commanders of the Great Army, a coalition of Norse warriors that in AD 865 invaded the Anglo-Saxon kingdoms of Northumbria, Mercia, East Anglia and Wessex. The First Viking Age in Ireland began in 795, when Vikings began carrying out hit-and-run raids on Gaelic Irish coastal settlements.  Over the following decades the raiding parties became bigger and better organized; inland settlements were targeted as well as coastal ones; and the raiders built naval encampments known as longphorts to allow them to remain in Ireland throughout the winter.  In the mid 9th century, Viking leader Turgeis or "Thorgest" founded a stronghold at Dublin, plundered Leinster and Meath, and raided other parts of Ireland.  He was killed by the High King, Máel Sechnaill mac Máele Ruanaid, which was followed by several Irish victories against the Vikings and the seizure of Dublin in 849.  Shortly after, a new group of Vikings known as the Dubgaill ("dark foreigners") came to Ireland and clashed with the earlier Viking settlers, now called the Finngaill ("fair foreigners").  The wavering fortunes of these three groups and their shifting alliances, together with the shortcomings of contemporary records and the inaccuracy of later accounts, make this period one of the most complicated and least understood in the fledgling city's history.  In 853 a Viking warlord called Amlaíb (, possibly Olaf the White) arrived and made himself king of Dublin.  He ruled along with his brothers Ímar ("Ívarr", possibly Ivar the Boneless) and Auisle ("Ásl").  For the next fifteen years or so, they used Dublin as their base for a series of campaigns against Irish kingdoms.  During these conflicts they briefly allied themselves with several Irish kings.  The Dublin Vikings also carried out a number of raids in Britain at this time.  The deaths of Ivar (c.873) and Olaf (c.874) were followed by internecine conflict among the Vikings.  Although intermittent warfare between the Vikings and the Irish continued, these inner conflicts weakened the Viking colonies and made it easier for the Irish to unite against them.  In 902, Cerball mac Muirecáin, king of Leinster, and Máel Findia mac Flannacáin, king of Brega, launched a two-pronged attack on Dublin and drove the Vikings from the city.  However, in 914 the Vikings now known as the Uí Ímair (House of Ivar) would return to Ireland, marking the beginning of the Second Viking Age. Tryggvi "the Pretender" (Old Norse "Tryggvi Ólafsson", Norwegian "Tryggve Olavsson") was a Viking chieftain who lived in the early eleventh century, and came from "west across the sea" (probably from the Norse settlements in England and Ireland).  His story appears in "Heimskringla" by Snorri Sturluson, the saga "Morkinskinna", and a saga composed by Oddr Snorrason on Olaf Tryggvason. Ivar the Boneless (Old Norse: "Ívarr hinn Beinlausi" ; ) was a Viking leader and a commander who invaded what is now England.  According to the "Tale of Ragnar Lodbrok", he was the son of Ragnar Lodbrok and Aslaug.  His brothers included Björn Ironside, Halfdan Ragnarsson, Hvitserk, Sigurd Snake-in-the-Eye and Ubba.
Answer: Ubba