Aelian was born in Praeneste, a town in the hills east of Rome famous for its ancient oracle and its temple of Fortuna, the Roman goddess of chance and fate, around the year 175 CE. His full name was Claudius Aelianus, and he was a Roman citizen by birth, not a Greek. Yet he chose to write in Attic Greek, the classical dialect of Athens that had been the language of the city's greatest writers centuries before his birth, and he cultivated a style so pure and so deliberately archaic that the later Suda records his nickname meliglossos, the honey-tongued. He lived in Rome during the reigns of the emperors Septimius Severus and Caracalla, the father and son who ruled the empire from 193 to 217 CE, but he seems never to have left Italy. His accounts of distant lands depended heavily on reading rather than personal travel.

His great work was De Natura Animalium, On the Characteristics of Animals, seventeen books that describe the habits of creatures from elephants to ants, from parrots to scorpions. The work is not a scientific treatise in the manner of Aristotle, the philosopher who had founded the study of biology centuries earlier through observation and classification. Aelian's method was anecdotal, moralising, and deeply rooted in mythology. He believed that animals possessed virtues that humans had lost, and he filled his pages with stories that blur the line between natural history and folklore. In his pages, the phoenix knows the passage of five hundred years, the halcyon calms the winter sea to lay its eggs, and the manticore, the man-eating monster with a human face and a scorpion tail that was first described by the Greek physician Ctesias at the Persian court, shoots its venomous stingers like arrows. For modern scholars, these passages are invaluable. They preserve fragments of the lost Indica of Ctesias, the Persian history of Dinon, and the paradoxography of Antigonus of Carystus, works that vanished long ago but survive in Aelian's quotations.

His other major work, Varia Historia, Miscellaneous History, is a collection of fourteen books of historical and biographical anecdotes, many of them mythological or quasi-mythological in nature. Here Aelian gathered stories about Pythagoras, the philosopher who believed in the transmigration of souls and who was said to possess a thigh of gold; about Alexander the Great, the Macedonian conqueror who claimed descent from heroes; and about Lycurgus, the Spartan lawgiver whose constitution made Sparta the most feared military power in Greece. He recorded the sayings of the Seven Sages, the wise men of archaic Greece, and he preserved details of religious rituals, athletic contests, and the private lives of philosophers that help preserve the texture of ancient traditions. The work is deliberately unsystematic, a cabinet of curiosities rather than a history, and that is precisely its value. Where a historian like Thucydides, the Athenian writer who chronicled the Peloponnesian War, sought causes and patterns, Aelian collected the glittering fragments.

Aelian's method has made him both frustrating and indispensable to modern scholars. He moves between named sources and anonymous reports, and the origins and reliability of individual anecdotes are not always easy to establish. Yet without him, entire traditions would be lost. His quotations from the lost works of the poet Ibycus, the historian Theopompus, and Clearchus, a pupil of Aristotle, are important witnesses to writings that no longer survive intact. His death is usually placed around 235 CE, near the end of the reign of the emperor Severus Alexander, and his works passed into the Byzantine manuscript tradition, the copying culture of the Eastern Roman Empire, where they were copied, excerpted, and eventually printed in the Renaissance. Renaissance printed editions carried his collections to new readers, and modern scholars continue to study and edit his Greek.