Notker the Stammerer (c. 840 – 6 April 912), Notker Balbulus, or simply Notker, was a Benedictine monk at the Abbey of Saint Gall active as a composer, poet and scholar. Described as "a significant figure in the Western Church", Notker made substantial contributions to both the music and literature of his time. He is usually credited with two major works of the Carolingian period: the Liber Hymnorum, which includes an important collection of early musical sequences, and an early biography of Charlemagne, the Gesta Karoli Magni. His other works include a biography of Saint Gall known as the Vita Sancti Galli and a martyrology, among others.

Born near the Abbey of Saint Gall, Notker was educated alongside the monks Tuotilo and Ratpert; all three were composers, making the Abbey an important center of early medieval music. Notker quickly became a central figure of the Abbey and among the leading literary scholars of the Early Middle Ages. A renowned teacher, he taught Solomon III, the bishop of Constance and on occasion advised Charles the Fat. Although venerated by the Abbey of Saint Gall and the namesake of later scholars there such as Notker Physicus and Notker Labeo, Notker was never formally canonized. He was given "the Stammerer" as an epithet, due to his lifelong stutter.

Notker was born around 840, near the Abbey of Saint Gall in modern-day Switzerland. His wealthy family was of either Alemannic or Swiss descent and they owned land in Jonschwil of Thurgau. Notker's later biographer Ekkehard V claims he was born in Heiligau—now Elgg—in the Canton of Zürich, but this has been rejected by the historian Gerold Meyer von Knonau [de], who suggests a birthplace near Jonschwil. Since childhood Notker had a stutter, because of tooth loss in his youth, resulting in the Latin epithet balbulus (lit. 'babbler') or "the Stammerer" in English. The German musicologist Stefan Morent [de] likened him to the partially blind Walafrid Strabo and Hermann of Reichenau, who had a limp, as three monks with physical impairments who achieved creative feats.

He began schooling at Saint Gall early in age and spent the rest of his life in the Abbey. His teachers included the Swiss monk Iso [de] and the Irish monk Moengal, called "Marcellus" by Notker. He may have also been instructed by Grimald of Weissenburg, a student of Alcuin. The later book Casus monasterii Sancti Galli of Ekkehard IV "paints a lively picture of the monastery school", and notes that Notker was taught alongside Tuotilo and Ratpert; all three would become teachers and composers at the Abbey.

Although first and foremost a scholar, Notker held numerous positions at the Abbey including librarian in 890 and master of guests (hospitarius) in 892 and 894. He became established as a well-known teacher and was eventually appointed "master of the monastic school". Among his students was Solomon, who was later Bishop of Constance from 890 until his death in 912. Notker was often called upon for council from outside the Abbey; on occasion he advised Charles the Fat who visited the Abbey from 4–6 December 883. Charles was the dedicatee of Notker's De Carolo Magno, an early biography of Charlemagne. Ekkehard IV lauded Notker as "delicate of body but not of mind, stuttering of tongue but not of intellect, pushing boldly forward in things Divine, a vessel of the Holy Spirit without equal in his time".

Despite his renown in the Abbey, Notker never became an abbot of Saint Gall, and repeatedly declined abbacy offers elsewhere. Notker died in Saint Gall on 6 April 912.

Notker created the Liber Hymnorum ("Book of Hymns") during the late 9th century, an important early collection of Sequences dedicated to Liutward, the bishop of Vercelli. Completed in 884, it is essentially a set of melodies and texts organized by the Church calendar. The oldest surviving sources of the Liber Hymnorum date from either Notker's last years or directly after his death.

In the preface to his Liber Hymnorum, Notker claimed his musical work was inspired by an antiphoner that was brought to Gall from the Jumièges Abbey, soon after its destruction in 851. Notker was particularly inspired by the Jumièges chant book setting verses to the melodies, making them easier to remember; he goes on to discuss his childhood difficulties in recalling the melodiae longissimae.