Mark Antony
Roman general and consul with Julius Caesar in 44 BCE, who proposed the law that renamed the month Quintilis July.
How the Romans fixed the year
Censorinus, On the Birthday 20–22 (238 CE), in the edition of Friedrich Hultsch (Leipzig, 1867) · 238 CE
ex his duodecim mensibus duorum tantum nomina inmutata. nam Quintilis Iulius cognominatus est C. Caesare V et M. Antonio cons. anno Iuliano secundo: qui autem Sextilis fuerat, ex SC. Marcio Censorino C. Asinio Gallo cons. in Augusti honorem dictus est Augustus anno Augusti vicensimo. quae nomina etiam nunc ad hanc permanent memoriam.
Of these twelve months, only two have had their names changed. Quintilis was renamed Iulius [July] when Gaius Caesar, for the fifth time, and Mark Antony were consuls, in the second Julian year. The month that had been Sextilis was renamed Augustus in honor of Augustus by a decree of the senate. That was when Marcius Censorinus and Gaius Asinius Gallus were consuls, in the twentieth year of Augustus. These names have lasted to our own day.
Where the months got their names
Macrobius, Saturnalia 1.12–14 (early fifth century CE), in the edition of Franz Eyssenhardt (Leipzig, 1893) · early fifth century CE; the dialogue is set in the 380s
Sequitur Iulius qui, cum secundum Romuli ordinationem, Martio anni tenente principium, Quintilis a numero uocaretur, nihilo minus tamen etiam post praepositos a Numa Ianuarium ac Februarium retinuit nomen, cum non uideretur iam quintus esse sed septimus. sed postea in honorem Iulii Caesaris dictatoris, legem ferente M. Antonio M. filio consule, Iulius appellatus est, quod hoc mense a. d. quartum Idus Quintilis Iulius procreatus sit.
Next comes July. Under Romulus's plan, when March began the year, it was called Quintilis from its number, "fifth." It kept that name even after Numa put January and February in front of it, though it no longer seemed to be the fifth month but the seventh. But later it was named Iulius in honor of Julius Caesar the dictator, under a law proposed by the consul Mark Antony, son of Marcus. The reason was that Julius had been born in this month, on the fourth day before the Ides of Quintilis.