Aristeas in Wikipedia
Aristeas (Greek: Ἀριστέας) was a semi-legendary Greek poet and miracle-worker, a native of Proconnesus in Asia Minor, active ca. 7th century BCE. In book IV of The Histories, Herodotus reports
"The birthplace of Aristeas, the poet who sung of these things, I have already mentioned. I will now relate a tale which I heard concerning him both at Proconnesus and at Cyzicus. Aristeas, they said, who belonged to one of the noblest families in the island, had entered one day into a fuller's shop, when he suddenly dropt down dead. Hereupon the fuller shut up his shop, and went to tell Aristeas' kindred what had happened. The report of the death had just spread through the town, when a certain Cyzicenian, lately arrived from Artaca, contradicted the rumour, affirming that he had met Aristeas on his road to Cyzicus, and had spoken with him. This man, therefore, strenuously denied the rumour; the relations, however, proceeded to the fuller's shop with all things necessary for the funeral, intending to carry the body away. But on the shop being opened, no Aristeas was found, either dead or alive. Seven years afterwards he reappeared, they told me, in Proconnesus, and wrote the poem called by the Greeks The Arimaspeia, after which he disappeared a second time. This is the tale current in the two cities above-mentioned. "
Aristeas was supposed to have authored a poem called the Arimaspea, giving an account of travels in the far North. There he encountered a tribe called the Issedones, who told him of still more fantastic and northerly peoples: the one-eyed Arimaspi who battle gold-guarding gryphons, and the Hyperboreans among whom Apollo lives during the winter.
Two hundred and forty years after his death, Aristeas appeared in Metapontum in Southern Italy to command that a statue of himself be set up and a new altar dedicated to Apollo, saying that since his death he had been travelling with Apollo in the form of a sacred raven.
This story appears to be referred to in Neil Gaiman's Sandman comics: Aristaeus was a man who lived around 700 BCE, and became, by transformation, one of the ravens acting as advisor to Dream.