William X. O'Brien
 William X. O'Brien (ITGWU) and William O'Brien (Home Rule/IPP) were contemporaries in Irish politics early in the 20th century but should not be confused. For other people of the same name see William O'Brien (disambiguation).William X. O'Brien (23 January 1881 – 31 October 1968) was a politician and trade unionist in Ireland.Born in Clonakilty County Cork O'Brien moved with his family to Dublin in 1897 and quickly became involved in the Irish Socialist Republican Party (ISRP).