Gregorios Xenopoulos (Greek: Γρηγόριος Ξενόπουλος [kseˈnopulos]; December 9, 1867 – 14 January 1951) was a novelist, journalist and playwright from Zakynthos.

His was the trademark signature "Σας ασπάζομαι, Φαίδων" ("Yours sincerely, Phaedon)", which he used in letters ostensibly addressed to the magazine.

He became a member of the Academy of Athens in 1931, and founded the Society of Greek Writers (Εταιρεία Ελλήνων Λογοτεχνών) together with Kostis Palamas, Angelos Sikelianos and Nikos Kazantzakis.

The family moved to Zakynthos soon after, where Gregorios spent his youth until 1883, when he enrolled in the University of Athens to study physics and mathematics.

He then turned for inspiration to his birthplace, Zakynthos, and as a result wrote some of his best novels, such as "Magaret Stefa" (1893) and Κόκκινος Βράχος (Kokkinos Vrachos, "Red Rock", 1905).

His work has been criticised for putting quantity ahead of quality, with many sequels, and for pandering to the tastes of his readers with scenes which were sexually provocative for the period.

His most famous theatrical plays are: "Το μυστικό της Κοντέσσας Βαλέραινας" (To mystiko tis kontessas Valerainas, "The Secret of Countess Valerena", 1904), "Στέλλα Βιολάντη" (Stella Violanti, 1909, with Marika Kotopouli), "Φοιτηταί", (Foititai, "Students").

In 1901 he played a leading part with Kostis Palamas in establishing the theatre "Nea Skini" and because of his fluency in many languages, he was aware of important intellectual developments in major European countries at that time.

In the magazine "Panathinaia" ("Παναθήναια"), he published a lot of reviews of famous Greek writers, such as Alexandros Papadiamantis, Demetrius Vikelas etc.