David was the youngest son of Vladimir I, Grand Duke of Russia, Olga was his great-grandmother. After Vladimir’s death, his half-brother Svyatopolk seized the capital Kiev and had First Boris, the older brother, and immediately afterwards Gleb killed. Sviatoslav, another brother, had fled to the Carpathians, but he also died under the knives of his henchmen. Of the brothers, only Yaroslav, who resided in Novgorod – today’s Nizhny Novgorod – got away with his life. In 1019 he defeated the army of Svyatopolk and chased him to the Tatras, where he died disgracefully. Yaroslav, later called the Sage, had thus avenged the murder of his brothers. In 1072, Gleb and Boris’ bones were transferred on May 2 to the newly consecrated Boris and Gleb Church in Vyshgorod/Vyshhorod near Kiev, a new translation took place in 1115. To this day, churches and monasteries in Russia are named after Boris and Gleb, the city of Borissoglebsk near Voronezh on the Don got its name after them. Gleb was probably canonized together with Boris on May 2, 1071 (or 1072), when her bones were transferred to the newly consecrated Boris and Gleb Church in Vyshhorod near Kiev.
They are the first saints of the Russian Church.
Joachim Schäfer: Artikel Gleb, aus dem Ökumenischen Heiligenlexikon: https://www.heiligenlexikon.de/BiographienG/Gleb.html