Gelou was the Vlach ruler of Transylvania at the time of the Hungarian conquest of the Carpathian Basin around 900 AD, according to the Gesta Hungarorum. Although the Gesta Hungarorum, which was written after 1150, does not indicate the enemies of the conquering Hungarians (Magyars) known from earlier annals and chronicles, it refers to local rulers—including Gelou—who are not mentioned in other primary sources. Consequently, historians debate whether Gelou was a historical person or an imaginary figure created by the unidentified author of the Gesta Hungarorum. In Romanian historiography, based on the mention of him by Anonymus some 300 years later, Gelou is considered one of three early-10th-century Romanian dukes with lands in the intra-Carpathian region of present-day Romania.

Vlach, also Wallachian, is a term and exonym used from the Middle Ages until the Modern Era to designate speakers of Eastern Romance languages living in Southeast Europe — south of the Danube and north of the Danube.