Giovanni Antonio (Giannantonio) Orsini del Balzo (9 September 1401 – 15 November 1463) was a southern Italian nobleman and military leader; he was Prince of Taranto, Duke of Bari, Count of Lecce, Acerra, Soleto and Conversano, as well as Count of Matera (1433–63) and of Ugento (1453–63).
Born in Lecce, he was the son of Raimondo Orsini del Balzo, Prince of Taranto, and Mary of Enghien, an heiress of the Brienne main branch. When his father died, he was one year old, and his mother married with King Ladislaus of Naples, who acquired all the family's possessions (1407).
In 1417 Giannantonio married Pope Martin V's niece Anna Colonna, daughter of the Prince of Amalfi. After James II' renounce, he received the Principality of Taranto from queen Joanna II of Naples on 4 May 1421. This act made him the most powerful baronial lord of the Kingdom of Naples, with lands including 7 archbishoprics, 30 bishoprics, 300 castles and extending from Salerno to Taranto.
Giannantonio was also an influent member of the Neapolitan court, and remained engulfed in the struggle between Joanna and Alfonso V of Aragon, whom he supported in the civil war against John II of Anjou. When Alfonso became king of Naples, Giannantonio further increased his power with the titles of Grand Constable and of Duke of Bari.
However, when Alfonso died, he retreated to Taranto to head a group of barons against the former's son, Ferdinand I, in favour of John II. After several feats of war, Giannantonio and his side were defeated, but in the end, he managed to become reconciled with the Aragonese king. He died in Altamura Castle in 1463,[1] strangled by a certain Paolo Tricarico, perhaps a royal killer. King Ferdinand confiscated most of his lands. His niece Isabella, the legitimate heiress of Giannantonio's lands, died soon afterwards in 1465. Her heir was her eldest son, the future Alfonso II of Naples.