Companion of Columbanus
Gall's life is bound up with that of Saint Columbanus, under whom he had trained at Bangor. Around 589 or 590 he was among the twelve companions who crossed from Ireland to the European continent with Columbanus, and the band settled first at Luxeuil in Gaul.
When Columbanus was driven into exile in 610, Gall followed him northward, traveling up the Rhine as far as Bregenz on Lake Constance. The two parted in 612: Columbanus pressed on into Italy, while Gall remained behind in Alemannia. According to the Wikipedia account, illness kept Gall from continuing, and he was cared for at Arbon.
Hermit and missionary in Alemannia
Remaining among the Alemanni of what is now eastern Switzerland, Gall established himself as a hermit in the forests southwest of Lake Constance, near the source of the River Steinach. There cells were built for twelve monks whom he instructed, and he came to be recognized as a powerful preacher throughout the region.
He twice declined high ecclesiastical office. When the See of Constance fell vacant, the clergy unanimously favored Gall as bishop, but he refused, citing the church law against electing foreigners. Around 625 the monks of Luxeuil asked him to take up the abbacy of their monastery after the death of Eustasius, and he declined this as well, preferring his solitary life despite his advanced age.
The Abbey and city of St Gallen
Gall reposed at Arbon at about ninety-five years of age, around 645 to 650. A church was raised at the site of his settlement, and before the middle of the eighth century it had developed into a proper monastery.
The Abbey of Saint Gall was formally established in 719, with Saint Othmar serving as its first abbot. The community became the nucleus of the Canton of St Gallen in eastern Switzerland, and Gall is honored as the founder of the city that grew up around it.
Veneration
Gall's feast is kept on 16 October. As a saint of the undivided Church before the schism, he is venerated in the Eastern Orthodox Church, the Roman Catholic Church, and the Church of Ireland.
By long tradition he is depicted in art accompanied by a bear, a reference to legendary accounts of his life in the wilderness.