Hasan Tahsin was the code name of Osman Nevres (1888 – 15 May 1919), a Turkish nationalist,[1][2] patriot, and journalist of Dönmeh descent.

A member of the Ottoman Special Organization, he unsuccessfully tried to assassinate Noel and Charles Roden Buxton in Romania during World War I.

[7] He was sentenced to five years imprisonment for the attempt but released when German forces overran Romania.

[8]: 75 He opened fire on the Greek soldiers who landed at Smyrna (present day İzmir) on 15 May 1919[9] in the opening act of the Greek occupation of more than three years that extended over a large part of western Anatolia, as well as of the Greco-Turkish War.

At the time of his death he had been publishing and writing for the newspaper Hukuk-u Beşer (Ottoman Turkish for Human Rights).