Booley (Japanese: ブーレイ Romaji: būrei) is the assassin responsible for murdering the late princess of Saillune, wife to Prince Philionel El Di Saillune and mother to both Gracia Ul Naga Saillune and Amelia Wil Tesla Saillune. The assassin had originally targeted Gracia, hoping to kill one of the possible heirs to the throne, but due to a case of mistaken identity, killed her mother instead. Gracia was a witness to her mother's murder, and killed Booley using the spell Chaos String.
It is highly suspected that it was the trauma of seeing her mother murdered and Booley's subsequent death that caused Gracia to leave home as Naga the Serpent.
While Booley never appears in Slayers stories directly, another former assassin who Naga confronts in the third Slayers Special novel boasts about his skills being "better than Booley's", suggesting that while alive, Booley had been an assassin of some notoriety.