In 1035 there arrived William Iron-Arm and Drogo, the two eldest sons of Tancred of Hauteville, a petty noble of the Cotentin in Normandy. The two joined in the revolt of the Lombards against Byzantine control of Apulia. By 1040 the Byzantines had lost most of that province. In 1042 Melfi was chosen as the Norman capital, and in September of that year the Normans elected as their count William Iron-Arm, who was succeeded in turn by his brothers Drogo, Comes Normannorum totius Apuliae e Calabriae ("the Count of all Normans in Apulia and Calabria"), and Humphrey, who arrived about 1044.
Robert Guiscard was the sixth son of Tancred of Hauteville and eldest by his second wife Fressenda. According to the Byzantine historian Anna Comnena, he left Normandy with only five mounted riders and thirty followers on foot. Upon arriving in Langobardia in 1047, he became the chief of a roving robber-band. Anna Comnena also leaves a physical description of Guiscard:
This Robert was Norman by descent, of minor origin, in temper tyrannical, in mind most cunning, brave in action, very clever in attacking the wealth and substance of magnates, most obstinate in achievement, for he did not allow any obstacle to prevent his executing his desire. His stature was so lofty that he surpassed even the tallest, his complexion was ruddy, his hair flaxen, his shoulders were broad, his eyes all but emitted sparks of fire, and in frame he was well-built ... this man's cry it is said to have put thousands to flight. Thus equipped by fortune, physique and character, he was naturally indomitable, and subordinate to no one in the world.
Lands were scarce in Apulia at the time and the roving Guiscard could not expect any grant from Drogo, then reigning, for Humphrey had just received his own county of Lavello. Guiscard soon joined Prince Pandulf IV of Capua in his ceaseless wars with Prince Guaimar IV of Salerno (1048). The next year, however, Guiscard left Pandulf, according to Amatus of Montecassino because Pandulf reneged on a promise of a castle and his daughter's hand. Guiscard returned to his brother Drogo and asked to be granted a fief. Drogo, who had just finished campaigning in Calabria, gave Guiscard command of the fortress of Scribla. Dissatisfied with this position, Guiscard moved to the castle of San Marco Argentano (after which he later named the first Norman castle in Sicily, at the site of ancient Aluntium). During his time in Calabria, Guiscard married his first wife, Alberada of Buonalbergo, the daughter of Lord Girard of Buonalbergo.
Guiscard soon rose to distinction. The Lombards turned against their erstwhile allies and Pope Leo IX determined to expel the Norman freebooters. His army was defeated, however, at the Battle of Civitate sul Fortore (1053) by the Normans, united under Humphrey. Humphrey commanded the centre against the pope's Swabian troops. Early in the battle Count Richard of Aversa, commanding the right van, put the Lombards to flight and chased them down, then returned to help rout the Swabians. Guiscard had come all the way from Calabria to command the left. His troops were held in reserve until, seeing Humphrey's forces ineffectually charging the pope's centre, he called up his father-in-law's reinforcements and joined the fray, distinguishing himself personally, even being dismounted and remounting again three separate times according to William of Apulia. Honored for his actions at Civitate, Guiscard succeeded Humphrey as count of Apulia in 1057, over his elder half-brother Geoffrey. In company with Roger, his youngest brother, Guiscard carried on the conquest of Apulia and Calabria, while Richard conquered the principality of Capua.
The Papacy, foreseeing the breach with the Holy Roman Emperor (the Investiture Controversy), then resolved to recognize the Normans and secure them as allies. Therefore at the Council of Melfi, on 23 August 1059, Pope Nicholas II invested Guiscard as duke of Apulia, Calabria, and Sicily, and Richard of Aversa as prince of Capua. Guiscard, now "by the Grace of God and St Peter duke of Apulia and Calabria and, if either aid me, future lord of Sicily", agreed to hold his titles and lands by annual rent of the Holy See and to maintain its cause. In the next twenty years he undertook a series of conquests, winning his Sicilian dukedom.
The fall of Reggio, after a long and arduous siege, and the subsequent capitulation of Scilla, an island citadel to which the Reggian garrison had fled, opened up the way to Sicily. Roger first led a tiny force to attack Messina but was repulsed easily by the Saracen garrison. The large invading force which could have been expected did not materialise, for Guiscard was recalled by a new Byzantine army, sent by Constantine X, ravaging Apulia. In January 1061, Melfi itself was under siege and Roger too was recalled. But the full weight of Guiscard's forces forced the Byzantines to retreat and by May Apulia was calm.
He returned in 1064, but bypassed Enna taking straight for Palermo. However, his campsite was infested with tarantulas and had to be abandoned. The campaign was unsuccessful this time, though a later campaign, in 1072, saw Palermo fall and for the rest of Sicily it was only then a matter of time.
Bari was reduced (April 1071), and the Byzantine forces finally ousted from southern Italy. The territory of Salerno was already Guiscard's; in December 1076 he took the city, expelling its Lombard prince Gisulf, whose sister Sichelgaita he had married. The Norman attacks on Benevento, a papal fief, alarmed and angered Gregory VII, but pressed hard by the emperor, Henry IV, he turned again to the Normans, and at Ceprano (June 1080) reinvested Guiscard, securing him also in the southern Abruzzi, but reserving Salerno.
Guiscard's last enterprise was his attack on the Byzantine Empire, a rallying ground for his rebel vassals, such as Henry, Count of Monte Sant'Angelo. In this enterprise Guiscard crossed swords with his most redoubtable opponent, the only one worthy of himself, in a clash of swords that would become legendary in the years after. In this struggle he met his nemesis in the person of the greatest man of the age: Emperor Alexius. He contemplated seizing the throne of the Basileus and took up the cause of Michael VII, who had been deposed in 1078 and to whose son his daughter had been betrothed. He sailed with 16,000 men of which 1,300 were Norman knights against the empire in May 1081, and by February 1082 had occupied Corfu and Durazzo, defeating the Emperor Alexius in front of the latter (Battle of Dyrrhachium, October 1081). He was, however, recalled to the aid of Gregory VII, besieged in Castel Sant'Angelo by Henry IV (June 1083).
Marching north with 36,000 men he entered Rome and forced Henry to retire, but a short-lived rebellion or seditious tumult (émeute) of the citizens led to a three days' sack of the city (May 1084), after which Guiscard escorted the pope to Rome. His son Bohemund, for a time master of Thessaly, had now lost the Byzantine conquests. Guiscard, returning with 150 ships to restore them, occupied Corfu and Kefalonia, but died along with 500 Norman knights of fever in the latter on July 15 1085, in his 70th year. He was buried in the Hauteville family mausoleum of the Trinity Abbey (SS. Trinità) at Venosa. The town of Fiscardo on Kefalonia is named after him.
Guiscard was succeeded by Roger Borsa, his son by Sichelgaita; Bohemund, his son by an earlier Norman wife Alberada, being set aside. He left two younger sons: Guy, Duke of Amalfi, and Robert Scalio, neither of whom made any trouble for their elder brothers. At his death Guiscard was duke of Apulia and Calabria, prince of Salerno and suzerain of Sicily. His successes had been due not only to his great qualities but to the "entente" with the Papal See. He created and enforced a strong ducal power which, however, was met by many baronial revolts, one being in 1078, when he demanded from the Apulian vassals an "aid" on the betrothal of his daughter. In conquering such wide territories he had little time to organize them internally. In the history of the Norman kingdom of Italy Guiscard remains essentially the hero and founder, though his career ended in "something of a dead end, while his nephew Roger II is the statesman and organizer.
Though his relationship with the pope was rocky, Guiscard preferred to be on good terms with the papacy and he made a gesture of abandoning his first wife in response to church law. Though the popes were often fearful of his growing power, they preferred the strong and independent hand of a Catholic Norman to the rule of a Byzantine Greek. Guiscard received his investment with Sicily at the hands of Pope Nicholas II, who feared the opposition of the Holy Roman Emperor to the Papal reforms more. Guiscard supported the reforms, coming to the rescue of a besieged Pope Gregory VII, who had once excommunicated him for encroaching on the territory of the Papal States. After the Great Schism of 1054, the polarized religious atmosphere served to strengthen Guiscard's alliance with papal forces, resulting in a formidable papal-Norman opposition to the Eastern Empire.
Such was Guiscard's martial and political success that Dante Alighieri recorded it in his Divine Comedy, placing his spirit in Heaven's sphere of Mars with history's greatest Christian warriors. In Inferno, Dante describes Guiscard's enemies as a field of mutilated shades stretching out to the horizon.
Married in 1058 or 1059 to Sichelgaita and had 8 children: