Who allied himself with Antonius Primus and later became a future emperor?

The individual who allied himself with Antonius Primus and later became emperor is Vespasian. In the context of Roman history, Antonius Primus was a significant general during the Year of the Four Emperors (69 AD), a tumultuous period marked by civil war following the death of Nero. Vespasian, who was a key figure in this power struggle, initially aligned himself with Antonius Primus to bolster his claims to power during this chaotic time.

Vespasian's support of Primus was instrumental in his rise, especially given that Primus was a key ally in successfully overthrowing the previous emperor, Vitellius. Following the successful campaign that led to his eventual elevation as emperor, Vespasian initiated a new dynasty known as the Flavian dynasty, which would have lasting impacts on Rome, including construction projects like the Colosseum.

This context is important to understanding Vespasian's strategic partnerships during the power transitions in Rome and signifies why he was a pivotal figure leading to the stabilizing of the empire post-Nero's rule. The other options, while notable figures in Roman history, do not have the same connection to Antonius Primus during this particular time frame.