Short answers, pulled from the story.
Postumus, whose full name was Marcus Cassianius Latinius Postumus, was a Roman commander of Batavian origin who ruled a breakaway state known to modern historians as the Gallic Empire from around 260 to 269. At its peak, his domain included Gaul, Germania, Britannia, and Hispania.
Postumus came to power after his troops crushed a Juthungian army and he distributed the recovered spoils to his legions rather than sending them to Saloninus, the son of Emperor Gallienus, as ordered. His soldiers proclaimed him emperor, besieged Cologne, and killed Saloninus and his prefect Silvanus after the city walls were breached.
Postumus established his capital in northern Gaul, most likely at Colonia Claudia Ara Agrippinensium, the city now known as Cologne, or at Augusta Treverorum, the city now known as Trier.
The Labours of Hercules was a series of gold coins issued in 268 in honor of Postumus's favored deity, Hercules. The series is particularly renowned among numismatists, as are several aurei from his reign that carry an unusual full-face portrait of Postumus rather than the standard profile view.
Postumus was killed by his own soldiers in 269 after he refused to let them sack Mogontiacum, the city now known as Mainz, which he had just recaptured from the usurper Laelianus. The mutineers then elevated a common soldier named Marius as the next emperor.
Postumus did not attempt to capture Rome or dislodge Gallienus from power, and scholars continue to debate whether he ever intended to. His stated priority was the defense of the Rhine frontier, and his administrative structures remained conventionally Roman rather than overtly separatist.