Lelio Francesco Maria Sozzini or simply Lelio (Latin: Laelius Socinus; 29 January 1525 – 4 May 1562), was an Italian Renaissance humanist and anti-Trinitarian reformer, and uncle of the better known Fausto Sozzini (Latin: Faustus Socinus) from whom the Polish Brethren and early English Unitarians came to be called "Socinians".
Lelio Sozzini was born at Siena. His family descended from Sozzo, a banker at Percenna (Buonconvento), whose second son, Mino Sozzi, settled as a notary at Siena in 1304. Mino Sozzi's grandson, Sozzino (d. 1403), was the founder of a line of patrician jurists and canonists, Mariano Sozzini the elder (1397–1467) being the first and the most famous, and traditionally regarded as the first freethinker in the family.
Lelio (who spelled his surname Sozzini, Latinizing it Socinus) was the sixth son of Mariano Sozzini the younger (1482–1556) by his wife Camilla Salvetti, and was educated as a jurist under his father's eye at Bologna. He told Melanchthon that his desire to reach the fontes juris led him to Biblical research, and hence to rejection of "the idolatry of Rome."
Lelio Sozzini gained some knowledge of Hebrew and Arabic (he gave a manuscript of the Qur'an to Bibliander) as well as Greek, but was never a laborious student. His father supplied him with means and, on coming of age, he repaired to Venice, the headquarters of the evangelical movement in Italy. A tradition - first published by Christopher Sandius in 1684 in his book Bibliotheca antitrinitariorum and Andrzej Wiszowaty in 1668 in his book Narratio Compendiosa - and amplified by subsequent writers makes him a leading spirit in alleged theological conferences called the Collegia Vicentina at Vicenza about 1546-1547.