Pliny the Younger
Pliny the Younger was the nephew of Pliny the Elder, and was visiting his uncle at Pompeii when his uncle died in the eruption. Pliny the Younger, however, did not die, and has left us the only eye-witness account of what the eruption was like. Pliny went on to become a fairly important politician in the Roman Empire under the emperor Trajan.
Trajan sent Pliny to be the governor of Bithynia (on the Black Sea) in 117 AD, where he had to run the province and make sure there were no revolts and everyone paid their taxes. While he was trying to keep order there, Pliny ran into some problems with the Christians which provide our first evidence that Christianity had become illegal.
Pliny was a great letter-writer, and he kept copies of many of his letters and later published them for everyone to read. Many of his letters have survived to the present day. They provide very useful information about the life of wealthy aristocrats in Rome during the Golden Age of the Roman Empire.