There's next to nothing to be said for Marius because his reign was so short. The historian Eutropius writing about a hundred years after his death records his reign as lasting all of three days. Aurelius Victor, another historian contemporary to Eutropius, has him murdered the following day. This is of course hyperbole as evidenced in the fact that relatively many coins of him survive. The man was a blacksmith and how he made the jump from that lowly career to becoming an emperor, however short his tenure, should be worth its own "Movie of the Week" award. He succeeded Laelianus, another short-lived emperor, when the undisciplined troops under his command were told to hold their positions following an initially successful attack on barbarian-controlled Mainz. The soldiers wanted to recover war loot and wouldn't be held back by Laelianus so they murdered him and named the head rabble-rouser, Marius, as their next emperor.
RIC 5, Cohen 6 AE Antoninianus Obv: IMPCMARIVSPFAVG; radiate head right.
Rev: CONCORDIAMILITVM; clasped hands.