Aaron Kosminski (born Aron Mordke Kozmiński; 11 September 1865 – 24 March 1919) was a Polish barber and hairdresser, and suspect in the Jack the Ripper case. Kosminski was a Polish Jew who emigrated from Congress Poland to England in the 1880s. He worked as a hairdresser in Whitechapel in the East End of London, where a series of murders ascribed to an unidentified figure nicknamed "Jack the Ripper" were committed in 1888. From 1891, Kosminski was institutionalised after he threatened his sister with a knife. He was first held at Colney Hatch Lunatic Asylum, and then transferred to the Leavesden Asylum.