Geiseric, whose name means "Caesar-king", was an illegitimate son of King Godigisel; he is assumed to have been born near Lake Balaton around the year 389. After his father's death, Geiseric was the second most powerful man among the Vandals, after the new king, his half-brother Gunderic. After Gunderic's death in 428, Geiseric was elected king. Brilliant and well-versed in the military arts, he immediately began to seek ways of increasing the power and wealth of his people, who then resided in the Andalusia region of Spain. The Vandals had suffered greatly from attacks from the more numerous Visigoths, and not long after taking power, King Geiseric decided to leave Spain to this rival Germanic tribe. In fact, he seems to have started building a Vandal fleet even before he raised to kinghood.
Taking advantage of a dispute between Boniface, Roman governor of North Africa, and the Roman government, Gaiseric ferried all 80,000 of his people across to Africa in 429. Once there, he won many battles over the weak and divided Roman defenders and quickly overran the territory now comprising modern Morocco and northern Algeria. His Vandal army laid siege to the city of Hippo Regius (where Augustine had recently been bishop - he died during the siege), taking it after 14 months of bitter fighting. The next year, Roman Emperor Valentinian III recognized Geiseric as king of the lands he and his men had conquered.
In 439, after casting a covetous eye on the great city of Carthage for a decade, he took the city, apparently without any fighting. The Romans were caught unaware, and Geiseric captured a large part of the western Roman navy docked in the port of Carthage. Added to his own burgeoning fleet, the Kingdom of the Vandals now threatened the Empire for mastery of the Mediterranean Sea. Carthage, meanwhile, became the new Vandal capital and an enemy of Rome for the first time since the Punic Wars. With the help of their fleet, the Vandals soon subdued Sicily, Sardinia, Corsica and the Balearic Islands. Geiseric strengthened the Vandal defenses and fleet, and regulates the positions of Arians and catholics. In 442 the Romans acknowledge the Carthaginian conquests, and furthermore recognised the Vandal kingdom as an independent country rather than one officially subsidiary to the Roman rule. The area in Algeria that had remained for the larger part independent of the Vandals turned from a Roman province into an ally.
For the next 30 years, Geiseric and his soldiers sailed up and down the Mediterranean, living as pirates and raiders. One legend has it that Geiseric was unable to mount a horse because of a fall he'd taken as a young man; so he assuaged his desire for military glory on the sea.
In 455, Roman emperor Valentinian III was murdered. The person who ordered his murder, Petronius Maximus, usurped the throne. Geiseric was of the opinion that these acts voided his 442 peace treaty with Valentian, and within weeks, on May 31, King Gaiseric and his men landed on Italian soil and marched on Rome, where Pope Leo I implored him not to destroy the ancient city or murder its inhabitants. Geiseric agreed and the gates of Rome were thrown open to him and his men. Maximus, who fled rather than fight the Vandal warlord, was killed by a Roman mob outside the city. Although history remembers the Vandal sack of Rome as extremely brutal (and their act made the word 'vandalism' a term for any group of wantonly destructive people), in actuality Geiseric honored his pledge not to make war on the people of Rome, and the Vandals did not do much destruction (or even any notable destruction) in the city; they did however take gold, silver and many other things of value away from the city. He also took with him Empress Eudoxia, Valentinian's widow, and her daughters, including Eudocia, who married Geiseric's son Huneric after arriving in Carthage, and many important people were taken hostage for even more riches.
In 468, Geiseric's kingdom was the target of the last concerted effort by the two halves of the Roman Empire. They wished to subdue the Vandals and end their pirate raids. But the Vandal king, against long odds, defeated the eastern Roman fleet commanded by Basilicus off Cape Bon. It has been reported that the total invasion force on the fleet counted 100,000 soldiers. The Romans abandoned the campaign and Geiseric remained master of the western Mediterranean until his death, ruling from the Strait of Gibraltar all the way to Tripolitania.
In his internal politics, Geiseric gave freedom of religion to the Catholics, but demanded (conversion to) Arianism from all his close advisors. The common folk had low taxes under his reign, most of the tax pressure was on the rich Roman families and the catholic clergy.