Vetranio. 350 AD. AE3. DN VETRA-NIO PF AVG, laureate, draped and cuirassed bust right. "A" behind bust, star in front. / CONCORDIA MILITVM, Vetranio standing facing, head left, holding labarum in each hand. A in left field, mintmark dot ASIS dot. RIC VIII Siscia 274; LRBC 1162; Sear 18903. 20mm 4.2 grams[

The coin just came in today, which prompted me to do a little research on this rare emperor. I was always under the impression that Vetranio took on patriotic duties and defended the empire from the evil usurper Magnentius (killed the western co-emperor Constans who was the brother of Constantius II). In fact, I was going to emphasize the fact that at least somebody had the honor and decency (at least since Diocletian) to abdicate power for the good of the empire.
However, further research kind of disappointed me. First sign of a power grab was that his coinage read Augustus, which leads me to think he had ulterior motives. Wouldn't he have just declared himself Caesar? I also read conflicting information on how he was declared emperor. Vetranio was the Magister Peditum in the Balkans and some say he promoted himself in support of Constantius II, while others say his troops declared him to be emperor and lastly Constantius himself bestowed the title.
In any case, further reading revealed that he made an alliance with Magnentius which they hoped to negotiate with Constantius II for a settlement. According to Wikipedia, ".the two presented a united front against Constantius II in their embassy to his court at Heraclea in Thrace, whither he had arrived from the Persian war. They offered him the senior title in the Empire, and Magnentius proposed to wed his daughter to Constantius, himself to marry Constantia the emperor's sister." In the end Vetranio, sided with Constantius II and after the defeat of Magnentius he stepped down and was allowed to retire in piece.
Sorry if I butchered this, I don't do great write ups. If anyone as anything to add or correct, please do so.