Diotima of Mantinea plays an important role in Plato's Symposium. Since our only source concerning her is Plato, we cannot be certain whether she was a real historical personage or merely a fictional creation. However, it should be noted that nearly all of the characters named in Plato's dialogues have been found to correspond real people living during the time in question.
In Plato's Symposium, Socrates says that Diotima was a seer or priestess who had, in Plato's youth, taught him "the philosophy of love". Socrates also claims that she had succeeded in convincing the gods to postpone the pestilence that besieged Athens for ten years.
Plato was thought by most 19th and early 20th century scholars to have based Diotima on Aspasia, the mistress of Pericles, so impressed was he by her intelligence and wit. This question is far from resolved, however, and some scholars have argued convincingly that Diotima was a historical figure.Wider, Kathleen. "Women philosophers in the Ancient Greek World: Donning the Mantle". Hypatia vol 1 no 1 Spring 1986. Part of her argument focuses on the point that all scholars who argued 'for' a fictitious Diotima were male, and most used as a starting point Smith's (Smith, Dictionary of Greek and Roman Biography and Mythology, 1870) uncertainty of her actual existence.