Arnaud Baille/Sicre was a cobbler in the Comté de Foix in the late thirteenth and early fourteenth century. A number of details about his life are known to us through the Fournier Register, and Emmanuel Le Roy Ladurie's analysis of those records.

Raised in Ax-les-Thermes he was the son of Arnaud Sicre, a notary, and Sybille Baille. His father was a Catholic and worked as a writer for the church. His mother, however, was a staunch Cathar. The marriage did not last long and at a young age Sybille forced her husband out of the house. Sybille returned to her maiden name while Arnaud Jr. and his brother Bernard would alternate between surnames, and sometimes use both. At the age of seven Arnaud was sent to join his father in Tarascon so that he could be educated.

His mother's heresy was discovered by the inquisition and she was arrested and later burned at the stake with the family property being confiscated. This left Arnaud much embittered as his mother's heresy had cost him his inheritance. By profession Arnaud thus became a transient cobbler.

In an effort to win back his family home Arnaud decided to become an informer for the inquisition. They sent him to Catalonia where a number of Cathar exiles were hiding. Arnaud joined with this group and eventually convinced a number of them to return to the Comté to attend his sisters wedding. The forces of inquisition were in wait and a number of the Cathars were caught including the parfait Bélibaste and the shepherd Pierre Maury.