Question: What Northumbrian missionary saint studied at Rath Melsigi?
Context: The Basilica of St. Francis Xavier is a parish church in the Archdiocese of Dubuque located in Dyersville, Iowa, United States.  The church was named in honor of the missionary Saint Francis Xavier.  It was raised to the status of a Minor Basilica in 1956.  The church and rectory were listed together on the National Register of Historic Places in 1999. Kimmage Mission Institute (KMI) was an educational institute of theology and cultures, founded 1991, by the Holy Ghost Fathers, at their Missionary College, in Kimmage Manor, Dublin.  The Holy Ghost Fathers had a long history of teaching Theology and Philosophy in Kimmage to its missionaries.  The KMI was developed as a response in the fall in vocations.  As well as the Spiritans, ten other missionary congregations were involved in the institute (they were the Divine Word Missionaries (SVD), Franciscan Missionary Sisters for Africa (FMA), Missionary Sisters of the Holy Rosary (MSHR), Medical Missionaries of Mary (MMM), Missionary Sisters of St. Columban, Missionary Society of Saint Columban (SSC), Missionary Sisters of Our Lady of the Apostolate (OLA), Redemptorist Congregation (CSsR), Society of African Missions (SMA) and Saint Patrick's Mission Society (SPS)). Rath Melsigi the monastery in Ireland during the 7th century where Saint Egelbert, an Anglo Saxon was educated.  Many Anglo Saxons and Frankish were educated at Irish monasteries, including King Alfred of England, Oswald of England & Dagobert II of France, to name a few.  It was located in what is now the townland of Clonmelsh, County Carlow.  Among those known to have studied there were Willibrord, Swithbert, and Egbert (639-729), who organised the mission to Frisia.  Others of the English community at Rath Melsigi included Adalbert of Egmond, Botolph and Chad of Mercia.  Others studied at Irish monasteries at Armagh, Kildare, Glendalough, and Clonmacnoise. Jove's Oak ("interpretatio romana" for Donar's Oak and therefore sometimes referred to as Thor's Oak) was a sacred tree of the Germanic pagans located in an unclear location around what is now the region of Hesse, Germany.  According to the 8th century "Vita Bonifatii auctore Willibaldi", the Anglo-Saxon missionary Saint Boniface and his retinue cut down the tree earlier the same century.  Wood from the oak was then reportedly used to build a church at the site dedicated to Saint Peter.  Sacred trees and sacred groves were widely venerated by the Germanic peoples. Saint Magnus of Füssen, otherwise Magnoald or Mang, was a missionary saint in southern Germany, also known as the Apostle of the Allgäu.  He is believed to have been a contemporary either of Saint Gall (died 627) or of Saint Boniface (died 754) and is venerated as the founder of St. Mang's Abbey, Füssen. Willibrord (Latin: "Villibrordus" ; 658 – 7 November AD 739) was a Northumbrian missionary saint, known as the "Apostle to the Frisians" in the modern Netherlands.  He became the first Bishop of Utrecht and died at Echternach, Luxembourg. Saint Adalbert of Egmond (also called Adelbert of Egmond) (died c. 710 in Egmond) was a Northumbrian Anglo-Saxon missionary.  He was one of Saint Willibrord's companions in preaching the gospel in Holland and Frisia. Sanjay Rath (Odia: ସଞୟ ରଥ ; born 7 August 1963 at Sambalpur, Odisha) is an Indian astrologer.  He comes from a traditional family of astrologers from Bira Balabhadrapur Sasan village in Puri, which trace their lineage back to Shri Achyuta Das (Acyutananda).  Sanjay Rath studied under his uncle, the late Pandit Kasinath Rath.  His grandfather, the late Pandit Jagannath Rath, was the Jyotish Ratna of Odisha and authored many books on Jyotisha. Saint Ninian is a Christian saint first mentioned in the 8th century as being an early missionary among the Pictish peoples of what is now Scotland.  For this reason he is known as the Apostle to the Southern Picts, and there are numerous dedications to him in those parts of Scotland with a Pictish heritage, throughout the Scottish Lowlands, and in parts of Northern England with a Northumbrian heritage.  In Scotland, Ninian is also known as Ringan, and as Trynnian in Northern England. Saint Vigor (French: "Saint Vigor, Vigeur" ; Latin: "Vigor, Vigorus" ) (died circa 537 AD) was a French bishop and Christian missionary.  An early "vita" was composed about 750-775, probably in Bayeux, where he had been bishop and was venerated from an early date.  Born in Artois, he studied at Arras under Saint Vedast.  His noble father, preoccupied with worldly prestige, would not grant approval for him to become a priest, so he ran away from home, taking nothing with him, accompanied by an accolyte, Theodimir.  Thereafter, he became a hermit preacher at Reviers, Calvados, and worked as a missionary.  Saint Vigor was named bishop of Bayeux in 514.
Answer: Willibrord