Auxilius was a Frank, who was ordained a priest, or perhaps only a deacon, in Rome by Formosus, and lived later in southern Italy, apparently at Naples.
Sergius had been a partisan of Stephen VI, and like the latter regarded the elevation of Formosus to the papacy as illegal and the orders conferred by him as null and void.
A third work of Auxilius, of similar import, was found by Mabillon and published by him under the title, "Libellus super causâ et negatio Formosi papæ", in his "Vetera Analecta".
In his "Auxilius und Vulgarius", quoted below, Ernst Dümmler published from a Bamberg manuscript two further writings of Auxilius, one of which is known as "In defensionem sacræ ordinationis papæ Formosi libellus prior et posterior", while the other bears in the manuscript itself the title: "Libellus in defensionem Stephani episcopi et præfatæ ordinationis".
In a necrology of the Abbey of Monte Cassino is noted on 25 January the death of an Auxilius, deacon and monk, author of a commentary on Genesis.