Didier Paton

Paton was a French spy tracking traitors for Maximilien de Robespierre during the French Revolution. At some point during his missions, Paton discovered proofs that uncovered the involvement of the Templar Order in the Revolution. Bringing his intel to his boss, Paton was thrown in jail for treason by Robespierre, who unknowingly to Paton was a Templar.

The Assassins then tasked Arno Dorian and one of his fellow brother to retrieve the notebook of the spy and to free Paton from his cell.

Reference

 * USGamer: Assassin's Creed: Unity preview