| Nerio I Acciaioli | |
|---|---|
 Nerio I as depicted in a late-17th-century book | |
| Lord/Duke of Athens contesting Peter the Ceremonious till 1387 | |
| Reign | 1385/1394–1394 |
| Predecessor | Peter the Ceremonious |
| Duke of Neopatras | |
| Reign | 1390–1393 |
| Predecessor | John the Hunter |
| Died | 17 September 1394 Athens, Duchy of Athens |
| Burial | |
| Spouse | Agnes de' Saraceni |
| Issue | Bartolomea Acciaioli Francesca Acciaioli (illeg.) Antonio I Acciaioli |
| House | Acciaioli |
| Father | Jacobo Acciaioli |
| Mother | Bartolomea Riccasoli |
| Religion | Roman Catholic |
Nerio I Acciaioli or Acciajuoli (full name Rainerio; died 25 September 1394) was the de facto Duke of Athens from 1385 to 1388, after which he reigned uncontested until his death in 1394. Born to a family of Florentine bankers, he became the principal agent of his influential kinsman, Niccolò Acciaioli, in Frankish Greece in 1360. He purchased large domains in the Principality of Achaea and administered them independently of the absent princes. He hired mercenaries and conquered Megara, a strategically important fortress in the Duchy of Athens, in 1374 or 1375. His troops again invaded the duchy in 1385. The Catalans who remained loyal to King Peter IV of Aragon could only keep the Acropolis of Athens, but they were also forced into surrender in 1388.
Nerio and his son-in-law, Theodore I Palaiologos, Despot of the Morea, occupied the Lordship of Argos and Nauplia. Nerio received Nauplia, but the Venetians expelled his troops from the town. Nerio was captured by a mercenary commander, Pedro de San Superano, in 1389. He was released after he promised to support the Venetians to seize Argos from Theodore I. He had to cede parts of his domains to Venice as a guarantee to keep his promise, but he could not convince his son-in-law to surrender Argos. Nerio's troops captured the Duchy of Neopatras from the Catalans in 1390, but the Ottoman sultan Bayezid I conquered the territory in 1393. Thereafter Nerio paid a yearly tribute to the sultan. King Ladislaus of Naples, who claimed suzerainty over Frankish Greece, invested Nerio with the Duchy of Athens on 11 January 1394. In his last will, Nerio distributed his domains between his younger daughter, Francesca, his illegitimate son, Antonio, and the church of Saint Mary (the Parthenon) of Athens.