Roger II or Roger the Great (Italian: Ruggero II, Sicilian: Ruggeru II, Greek: Ρογέριος; 22 December 1095 – 26 February 1154) was King of Sicily and Africa, son of Roger I of Sicily and successor to his brother Simon. He began his rule as Count of Sicily in 1105, became Duke of Apulia and Calabria in 1127, then King of Sicily in 1130 and King of Africa in 1148.

By 999, Norman adventurers had arrived in southern Italy. By 1016, they were involved in the complex local politics, where Lombards were fighting against the Byzantine Empire. As mercenaries they fought the enemies of the Italian city-states, sometimes fighting for the Byzantines and sometimes against them, but in the following century they gradually became the rulers of the major polities south of Rome. ^{[citation needed]}

Roger I ruled the County of Sicily at the time of the birth of his youngest son, Roger, at Mileto, Calabria, in 1095. Roger I's nephew, Roger Borsa, was the duke of Apulia and Calabria, and his great nephew, Richard II of Capua, was the prince of Capua. Alongside these three major rulers were a large number of minor counts, who effectively exercised sovereign power in their own localities. These counts at least nominally owed allegiance to one of these three Norman rulers, but such allegiance was usually weak and often ignored.

When Roger I died in 1101, his young son Simon became count, with his mother Adelaide del Vasto as regent. Simon died four years later in 1105 at the age of 12. Adelaide continued as regent to her younger son Roger, who was nine.

Upon the death in 1105 of his elder brother, Simon of Hauteville, Roger inherited the County of Sicily under the regency of his mother, Adelaide del Vasto, and his brother-in-law, Robert of Burgundy (d. 1112), son of Robert the Old. His mother was assisted by such notables as Christodulus, the Greek emir of Palermo. In 1109, Byzantine Emperor Alexios I Komnenos bestowed upon him the title of protonobilissimos in recognition of his knowledge of the Byzantine court. In the summer of 1110, Roger was visited by the Norwegian king Sigurd the Crusader, who was on his way to Jerusalem. The story in Icelandic sources suggests that Sigurd called Roger the king of Sicily twenty years before the latter actually obtained this title.

In 1112, at the age of sixteen, Roger began his personal rule, being named "now knight, now count of Sicily and Calabria" in a charter document dated 12 June 1112. In 1117, his mother, who had married Baldwin I of Jerusalem, returned to Sicily, since the patriarch of Jerusalem had declared the marriage invalid. Roger seems to have felt the slight, and this might explain his later reluctance to go crusading. Roger married his first wife, Elvira, daughter of King Alfonso VI of Castile and, later, his fourth wife, Isabella, who may be identical to his former concubine, the converted Moor, Zaida, who was baptized with the name of Isabella.

In 1122, Duke William II of Apulia, who was fighting with Count Jordan of Ariano, offered to renounce his remaining claims to Sicily as well as part of Calabria. Roger, in exchange, provided William with 600 knights and access to money for his campaign.

When William II of Apulia died childless in July 1127, Roger claimed all Hauteville family possessions in the peninsula as well as the overlordship of the Principality of Capua, which had been nominally given to Apulia almost thirty years earlier. However, the union of Sicily and Apulia was resisted by Pope Honorius II and by the subjects of the duchy itself.