Antonio I Acciaioli (also spelled Acciaiuoli or Acciajuoli), called the Bastard, was the illegitimate son of Nerio I of Athens and his longtime mistress Maria Rendi. He became Duke of Athens on the death of his father (1394), but was expelled within the year by the Republic of Venice, the executor of Nerio's will. During his warlike career as duke from 1402 to his death, he was a terror to his neighbours, but kept his domains internally peaceful.
By his father's will he inherited the castle of Livadeia and the government of the city of Thebes. He supported Theodore I Palaeologus, Despot of Morea, against the Despot of Epirus, Carlo I Tocco. In 1397, he invaded Attica with expansionist intentions.
In 1400, Venice appointed one of her own, Nicolò Vitturi, podestà in Athens. In 1402, Antonio besieged the city and took it, being proclaimed duke by the populace. In August, Venice offered 8,000 hyperpers for the city and in November Tommaso Mocenigo was sent to offer 1,700 ducats. In January or February 1403, Vitturi finally surrendered the castle and in that latter month, Bernardo Foscarini, the Venetian bailiff of Negroponte was captured in battle. On 31 March 1405, a peace treaty was signed between Antonio and Venice.
Antonio died still in power in January 1435 without legitimate children and his succession to the duchy was disputed between his nephews Nerio II and Antonio II, and his widow.