Rupert was from Liège, and late in life became abbot of the Abbey of Deutz,in what is now a suburb of Cologne. His was a prolific writer, and his works take up four volumes in Patrologia Latina (vols. 167–170); they include:
His works were later scrutinized in relation with the doctrine of impanation, a Eucharistic heresy according to the Roman Catholic Church because, contrary to the dogma of transubstantiation wherein the substance (but not the appearances and physical characteristics) of the bread and wine is wholly converted into the substance of Christ's Body and Blood, united to his divine person, impanation maintains that Christ directly unites the substance of the bread and wine to his divine person (or sometimes to his human nature), just as he united his own body and blood to his divine person. They influenced the theology in particular of Honorius Augustodunensis and Gerhoch of Reichersberg.