Herensuge is the name for dragon in Basque language. In Basque mythology, dragons appear sparingly, sometimes with seven heads. Only the god Sugaar is associated with this creature but more often with a serpent.
Yet there is a Christian legend in which certain Navarrese knight, Teodosio de Goñi, while making penance for double parricide in the Aralar Range has to rescue a woman that had been given as ransom to the dragon. When the chains that tie his ankles have been bitten by the dragon and he sees no way of defeating it, the knight prays to Saint Michael to save him. In Heaven, the archangel is notified: "Michael, they call you in Earth" but he replies: "My Lord, I won't go to that fight without You". Finally, the archangel, with God over his head appears and cuts the head of the dragon, liberating Teodosio from his chains and ending his penance.
This legend is specifically associated to the monastery of San Miguel de Aralar. It has been interpreted in the sense of justifying the break away with the religion and customs of Pagan Basques and adopting Christianity and, specifically, the veneration for St. Michael. For the rest, it is very similar to other European legends of knights and dragons, of which is surely a local adaptation.