Lucien Lachance was a legendary member of the Dark Brotherhood during the time leading to the Oblivion Crisis, at the end of the Third Era. A member of the Black Hand, he served as a Speaker, delivering contracts and recruiting new members. He also served as a troubleshooter, eliminating problems that appeared in the ranks or specific dangers to the Brotherhood. He operated out of an abandoned Imperial Fortress, Fort Farragut, just outside the city of Cheydinhal in Cyrodiil, which was the location of the local Dark Brotherhood Sanctuary.
Shortly after presiding over the cleansing of the Cheydinhal Sanctuary by his recently-recruited protege, Lachance was framed as a traitor by a malcontent within the Black Hand and executed by his colleagues in northern Cyrodiil. As the Listener of the Brotherhood had also been slain (mistakenly by this same protege), this recently-recruited individual then became the Listener.
Three centuries later, the spectre of Lucien Lachance was made available at need to successful assassins at the last remaining stronghold of the Dark Brotherhood in southwestern Skyrim. Lachance's spectre is known to remark upon events and circumstances in the living world, indicating the cryptic will of Sithis according to his own observations of energies in the Void. The spell enabling this summoning is known by the same name by which Lachance is now known: Spectral Assassin.