This solidus and a few other coins are the only known images of Romulus Augustulus (AD 475-476), the last Western Roman Emperor (unless you see him as a usurper, which makes Julius Nepos the last emperor ...). He 'reigned' ten months, if you can reign as a twelve year old boy put on the throne by your father, and was then 'retired' rather than killed by Odoacer.
It's difficult to write a biography of such a short life, but Adrian Murdoch has made a very impressive stab at it with The Last Roman: Romulus Augustulus and the Decline of the West gathering together the few facts known about this boy-emperor and setting them in the context of his time. The Last Emperor's public life was short, and so is this book - a welcome relief in an era when literally heavy (and often unreadable) biographies are the fashion. It's well written, easy reading, and beautifully portrays life at the time of the fall of the Roman empire in the West.