Lucius Appuleius Saturninus (died December 100 BC) was a Roman populist and tribune; he was a political ally of Gaius Marius, and his downfall caused a great deal of political embarrassment for Marius, who absented himself from public life until he returned to take up a command in the Social War of 91 to 88 BC.
As quaestor (104 BC) he superintended the imports of grain at Ostia, but was removed by the Roman Senate (an unusual proceeding), and replaced by Marcus Aemilius Scaurus, one of the chief members of the Optimates. He does not appear to have been charged with incapacity or mismanagement, and the standard view is that the injustice of his dismissal drove him into the arms of the Populares.
In 103 BC he was elected tribune. He entered into an agreement with Gaius Marius, and in order to gain the favour of his soldiers proposed that each of his veterans should receive an allotment of 100 iugera of land in the Roman province of Africa. He was also chiefly instrumental in securing the election of Marius to his fourth consulship (102 BC).
An opportunity to retaliate against the Nobiles was afforded him by the arrival (101 BC) of ambassadors from Mithridates VI of Pontus, with large sums of money for bribing the Senate; compromising revelations were made by Saturninus, who insulted the ambassadors. He was brought to trial for violating the law of nations, and only escaped conviction by an ad misericordiam appeal to the people. To the first tribunate of Saturninus is probably to be assigned his law on majestas, the exact provisions of which are unknown, but its object was probably to strengthen the power of the tribunes and the Populares; it dealt with the minuta majestas (diminished authority) of the Roman people, that is, with all acts tending to impair the integrity of the Commonwealth, being thus more comprehensive than the modern word "treason".