Question: The Prince-Archbishopric of Salzburg was founded in 739 by which leading figure in the Anglo-Saxon mission to the Germanic parts of the Frankish Empire during the 8th century?
Context: Prior to the arrival of Christianity, the ancestors of the Dutch observed a form of Germanic paganism augmented with various Celtic elements, due to the close proximity of various Celtic tribes and the general cultural blend of the region.  At the start of the 6th century the first (Hiberno-Scottish) missionaries arrived.  They were later replaced by Anglo-Saxon missionaries, who eventually succeeded in converting most of the inhabitants to Catholic Christianity by the 8th century.  Germanic/Frankish mythology influenced Christianity, and various stories of Dutch folklore can trace origins to it. The Frisian–Frankish wars were a series of conflicts between the Frankish Empire and the Frisian kingdom in the 7th and 8th centuries. Bavaria Slavica is a historiographic term used denote the areas populated by West Slavic people (Wends) between 6th and 12th century in Northeastern Bavaria.  The Wends settled in Bavaria in several waves between the 6th and ninth centuries and later in the 10th/11th century.  The settlement of loyal West Slavic Wends (and other minor) tribes was favoured under Frankish emperor Charlemagne.  Later the East Frankish Empire also settled largely Christianized Wends in rural or unpopulated regions or regions threatened by uprisings.  After the migration stopped they were quickly assimilated by the local Franks, who had always continued to form the majority, and by Bajuvarians. Frankish (reconstructed Frankish: "*Frenkisk"), Old Franconian or Old Frankish was the West Germanic language spoken by the Franks between the 4th and 8th century.  The language itself is poorly attested, but it gave rise to numerous loanwords in Old French.  Old Dutch is the term for the Old Franconian dialects spoken in the Low Countries, ie.  in present-day Belgium, in the present Netherlands and Western parts of today's Germany until about the 12th century when it evolved into Middle Dutch. The Saxons (Latin: "Saxones" , Old English: "Seaxe" , Old Saxon: "Sahson" , Low German: "Sassen" , German: "Sachsen" , Dutch: "Saksen" , Welsh: "Saeson" ) were a group of Germanic tribes first mentioned as living near the North Sea coast of what is now Germany (Old Saxony), in the late Roman empire.  They were soon mentioned as raiding and settling in many North Sea areas, as well as pushing south inland towards the Franks.  Significant numbers settled in large parts of Great Britain in the early Middle Ages and formed part of the merged group of Anglo-Saxons who eventually organised the first united Kingdom of England.  Many Saxons however remained in Germania (Old Saxony c. 531-804), where they resisted the expanding Frankish Empire through the leadership of the semi-legendary Saxon hero, Widukind.  Initially, Saxons of Britain and those of Old Saxony (Northern Germany) were both referred to as 'Saxons' in an indiscriminate manner.  The term Anglo-Saxon, in turn, came into practice in the 8th century (probably by Paul the Deacon) to distinguish English Saxons from continental Saxons (Ealdseaxe, 'old Saxons'). Anglo-Saxon missionaries were instrumental in the spread of Christianity in the Frankish Empire during the 8th century, continuing the work of Hiberno-Scottish missionaries which had been spreading Celtic Christianity across the Frankish Empire as well as in Scotland and Anglo-Saxon England itself during the 6th century (see Anglo-Saxon Christianity). A stem duchy (German: "Stammesherzogtum" , from "Stamm", meaning "tribe", in reference to the Germanic tribes of the Franks, Saxons, Bavarians and Swabians) was a constituent duchy of the kingdom of Germany at the time of the extinction of the Carolingian dynasty (the death of Louis the Child in 911) and the transitional period leading to the formation of the Holy Roman Empire later in the 10th century.  The Carolingians had dissolved the original tribal duchies of the Frankish Empire in the 8th century.  As the Carolingian Empire declined in the late 9th century, the old tribal areas assumed new identities as the subdivisions of the realm.  These are the five stem duchies (sometimes also called "younger stem duchies" in reference to the pre-Carolingian tribal duchies): The Prince-Archbishopric of Salzburg (German: "Fürsterzbistum Salzburg" ) was an ecclesiastical principality and state of the Holy Roman Empire.  It comprised the secular territory ruled by the Archbishops of Salzburg, as distinguished from the much larger Catholic diocese founded in 739 by Saint Boniface in the German stem duchy of Bavaria.  The capital of the archbishopric was Salzburg, the former Roman city of "Iuvavum ". The Hiberno-Scottish mission was a series of missions and expeditions initiated by various Irish clerics and cleric-scholars who, for the most part, are not known to have acted in concert.  There was no overall coordinated mission, but there were nevertheless sporadic missions initiated by Gaelic monks from Ireland and the western coast of modern-day Scotland, which contributed to the spread of Christianity and established monasteries in Britain and continental Europe during the Middle Ages.  The earliest recorded Irish mission can be dated to 563 with the foundation of Iona by the Irish monk Saint Columba.  Columba is said by Bede and Adamnán to have ministered to the Gaels of Dál Riada and converted the northern Pictish kingdoms.  Over the next centuries more missions followed and spread through Anglo-Saxon England and the Frankish Empire.  The early missions are often associated with the Christian practice known as Celtic Christianity, which was distinguished by its organizations around monasteries rather than dioceses and certain idiosyncratic traditions, but the desire to maintain a relationship with the Holy See saw their missions take on a more Roman character. Saint Boniface (Latin: "Bonifatius" ; 675 – 5 June 754 AD), born Winfrid, Wynfrith, or Wynfryth in the kingdom of Wessex in Anglo-Saxon England, was a leading figure in the Anglo-Saxon mission to the Germanic parts of the Frankish Empire during the 8th century.  He established the first organized Christianity in many parts of Germania.  He is the patron saint of Germania, the first archbishop of Mainz and the "Apostle of the Germans".  He was killed in Frisia in 754, along with 52 others.  His remains were returned to Fulda, where they rest in a sarcophagus which became a site of pilgrimage.  Facts about Boniface's life and death as well as his work became widely known, since there is a wealth of material available—a number of "vitae", especially the near-contemporary "Vita Bonifatii auctore Willibaldi", and legal documents, possibly some sermons, and above all his correspondence.
Answer: Saint Boniface