The central villain of the Jojo's Bizarre Adventure series, Dio is an immortal vampire and the arch rival of the Joestar clan.
He possesses a Stand known as The World, which has the combined powers of every Stand user born into the Joestar bloodline after the death of his enemy Jonathan Joestar (who's body Dio currently inhabits after he had his severed head sewn on Johnathan's corpse).
Series 1: Phantom Blood
Dio is the son of Dario Brando, an alcoholic and abusive father. Back when Dio was just a boy, he was brought into the household of George Joestar after the mysterious death of his father, so as to repay the debt he owed Dio's father for saving his life. But soon Dio's personality caused trouble for George's young son, Jonathan Joestar. Even more of a sociopath than his father, Dio was resolute to shatter Jonathan's spirit and take his place as the favored son, even going so far as to arrange for Jonathan's dog Danny to be burned to death.
Initially, Dio is able earn the trust of the patriarch of the Joestar family through deceit (and at Jonathan's expense). However, his plans of taking over the Joestar household were discovered by Jonathan when he discovered that not only had Dio poisoned his biological father to death, he was doing the same to his adoptive father, all to take the Joestar estate for his own.
Determined not to be stopped, and understanding the potential to enjoy power over all things instead of just the Joestar estate, Dio wears and activates the Stone Mask, becoming a nearly unstoppable vampire. His seemingly supernatural abilities are similar to the Mythical powers of the Mayan blood gods. He is able to walk on walls, and regenerate his body faster than fire can consume it. He is able to pressurize liquid in his eyeballs and then create small openings on pupils, eventually creating two fluid jets powerful enough to slice stone and kill living things. He is also able to vaporize his body fluid rapidly enough to freeze anything he touches. However, this is at the expense of having his body be sustained by sheer willpower alone, rather than vital energy. A sufficiently powerful vital force--specifically, sunlight or the Hamon force--will negate the sustaining force's presence and disintegrate the long-unliving body. Like all Jojo vampires, Dio sucks blood through tentacles in his fingers and has been seen at least once drinking blood from an unnamed girl.
At the end of Series 1, Dio's body was destroyed, but his severed head managed to kill Jonathan Joestar and together they sank to the bottom of the Atlantic Ocean.
Series 3: Stardust Crusaders
The anime series and video game are based on this third arc, which occurs about 100 years later. At the bottom of the sea, Dio's severed head reattached itself to Jonathan Joestar's lifeless body (giving Dio the same star birthmark as the members of the Joestar family). Dio's casket is recovered by fishermen, who are implied to have been killed by Dio as he awakened. He finds that he is now in the year 1985. After he returns to land he develops a Stand (a sort of ghostly bodyguard), giving him vastly powerful new abilities on top of his vampiric powers. For most of Series 3, Dio is out of scene and in the shadows, and the question of exactly what his Stand "The World" can do is a mystery.
In Series 3, many of Dio's offensive vampiric abilities do not appear, though he displays a new ability described as "evil implants"; parasites generated in his hair that attach themselves to and brainwash victims, finding early success with Kakyoin and Polnareff (In the fighting game JoJo's Bizarre Adventure it is the vector of attack in the move called "Charisma"). Dio's Stand "The World", as a sort of brother power to "Star Platinum", possesses great speed and strength and, crucially, is able to stop time, making Dio appear to teleport or move at impossible speed. Dio's ambition is to create a perfect world for himself and his servants. In the interim, he seeks to drain for himself the blood of the Joestar lineage, which will help him to fully fuse with Jonathan Joestar's body and take better control of The World. Once he does this, his powers will gradually increase, until he is able to stop time for as long as he likes.
The duel between The World and Star Platinum in Cairo
In the beginning of the story arc Dio's World, Dio mainly battles Kakyoin and Joseph. Kakyoin succeeds in leading Dio into a vast barrier created by his Stand, trapping him. Dio uses The World to stop time, allowing him to ignore the barrier and approach Kakyoin to deliver a fatal blow. Before dying, Kakyoin deduces the The World's time-stop ability and uses his last strength to give Joseph this message. Joseph then warns this to Jotaro before he is also killed by Dio.
After a long battle between Dio and Jotaro, Jotaro finds his own ability to stop time just before Dio drops a steamroller on him, proceeding in time-stop to break Dio's leg. Jotaro's intention was for the two to end the fight with a final blow once Dio's leg had healed. Dio, determined not to lose, squirts blood from his open leg into Jotaro's eyes. Dio then attempts a final kick with The World, which Jotaro blindly counters with a punch from Star Platinum. Star Platinum's hand breaks on The World's leg, but the punch sends a fissure through The World and through Dio, shattering Dio completely above the waist. Jotaro and doctors from the Speedwagon Foundation (an oil and medicine company loyal to the Joestar family) transfer the blood from Dio's lower half to Joseph Joestar, reviving him. Later, they lay Dio Brando's remains in the Sahara Desert to evaporate with the rising sun.
Series 6: Stone Ocean
In Part 6, it is revealed to the Joestars that his re-emergance was planned to create a perfect world when the moon reached a certain angle and time. He stumbled upon Enrico Pucci not long before Part 3 and "healed" his disfigured foot for him. After piercing Pucci with a Stand arrow, the two spent considerable time together, plotting and scheming. He questioned Pucci's loyalty to him, wondering why he didn't use Whitesnake to remove The World from him. Pucci had explained that he loved Dio as he had loved God, and thus worshipped him too much to betray him. Ensuring that he wouldn't completely fade, he left one of his bones in Pucci's care. Dio's presence continues to haunt the series, emerging in flashbacks and his disfigured sons. His bone played a vital plot element for the first half of Part 6, an odd green baby inheriting a Stand to merge with it.