(!) May contain headcanon!

Spoilers!!

Dio Brando (ディオ・ブランドー, Dio Burandō), known as DIO from Part 3 onwards, is the main antagonist in the original JoJo's Bizarre Adventure universe, primarily featured as the main antagonist in Phantom Blood and Stardust Crusaders, and a key posthumous antagonist in Stone Ocean.

After becoming a Vampire and later a Stand user, Dio gathered around him many minions and is responsible for many major events in the series, from the death of Jonathan Joestar to the Joestar Family's sudden acquisition of Stand power, and his legacy persists throughout the series. He is the wielder of the immensely powerful 「The World」.

Dio is the father of Giorno Giovanna, the protagonist of Part 5, as well as a handful of other illegitimate children.

Source: https://jjba.fandom.com/en-us/wiki/Dio_Brando