Adalbert was a preacher in 8th century Gaul. He claimed that an angel had conferred miraculous powers on him at his birth and that another had brought him relics of great sanctity from all parts of the earth. He also claimed to be able to see the future and read people's thoughts, telling those who came to him that they had no need to confess, since he knew what they had done, and that their sins were forgiven.
Adalbert appeared in the district of Soissons sometime in the 8th century and practised and preached a life of Apostolic poverty. He was banned by the local bishop from preaching in churches, and preached in the countryside, in the open air and later in churches that his followers (he had acquired many of them) had built for him.
According to St Boniface, he erected crucifixes at fields and springs. According to the same saint, Aldebert had also claimed to have received a letter that Jesus Christ had given from heaven to Jerusalem, which Aldebert used in his own preachings.
He also used mystic prayers of his own composition to call on the names of angels that were not accepted by the church canon (Uriel, Raguel, Tubuel, Adinus, Tubuas, Sabaoc and Simiel), and which his detractors alleged were demons that he invoked (some of these angel names also had gnostic connections). One of his prayers invoked by name the angel Raguel. His "miracles" gained him the awe of the people and he began to give away parings from his nails and locks of his hair as powerful amulets. He managed to get 'unlearned' (indoctri) bishops to consecrate him a bishop. He would erect crosses or build small chapels in the countryside and at springs and ordered public prayers to be said there.
Adalbert gained many followers and Boniface had written to Rome asking for the Pope to help him "lead back into the right path the people of the Franks and the Gauls" and that Aldebert had seduced the multitudes. St Boniface appealed to the Pope for a synod, which was then granted in 744 a synod in Soissons, with the help of Carloman and Pepin. The synod, led by Boniface, decided to take Aldebert into custody. The Synod ordered the burning of the crosses that Aldebert had set up in the countryside. However Aldebert escaped and continued to preach. A German synod the following year, presided by Boniface and Carloman, excommunicated him along with an Irish preacher named Clement and many others.
This was still not effective, however, as they continued to preach. Pope Zachary held another council in Rome in 745 to deal with Adalbert. Before the council was both Boniface's account and biography personally approved by Adalbert (neither Boniface nor Aldebert were actually present at the Council). Although the decisions of the northern councils that condemned him were upheld by the Roman council, they did not accede to Boniface's written wishes to have him excommunicated. The Council thought him to be a lunatic (as opposed to a charlatan) and decided he should be given a chance to repent, rather than be given excommunication (the Irish preacher's excommunication was upheld, however). The Synod ordered his writings (his approved biography, his prayer, and his supposed letter from Jesus) to be burned.
He was still active in 746; King Pepin sent an embassy to Rome to report that the heretics were still at large and still preaching. Pope Zachary, sent a letter to Boniface in 747 calling for a new council where both Boniface and Adalbert should attend, and that if the council found Adalert to be a heretic, that Adalbert should then be sent to him so that he could personally judge the case.
A century later, the Anonymous of Mainz wrote that Aldebert had been condemned and deposed at a Synod at Mainz (which may have been the council that Pope Zachary had called for), and that afterwards he was imprisoned for blasphemy in the monastery of Fulda. The same account reported that he later escaped and was killed by thieves, although he may have rather died in jail. He wrote an account of his own life, but only a fragment survives. St Boniface also wrote about him, and left the largest extant record of him.