Alexandre Jacob (September 29, 1879 – August 28, 1954), known as Marius Jacob, was a French anarchist illegalist. A clever burglar equipped with a sharp sense of humour, capable of great generosity towards his victims, he became one of the models for Maurice Leblanc's character Arsene Lupin.
Jacob was born in 1879 in Marseille to a working-class family. At the age of twelve, he signed up as a sailor's apprentice for a voyage that would carry him to Sydney where he deserted from the crew. Of his voyage he would later say, "I saw the world; it is not beautiful". After a short episode of piracy, which he soon rejected as too cruel, he returned to Marseilles in 1897 and gave up navy life definitively, plagued by fevers which would accompany him for the rest of his life. As an apprentice typographer he attended anarchist meetings and met his future wife Rose.
The parliamentary socialists of the late 19th century were opposed, often violently, to anarchists in the working world. Socialists sought to attain power legally through the electoral process. Anarchists, however, felt that social justice was not something that could be attained through the existing power structure, but instead had to be seized by the working classes. In the Europe of the Belle Epoque, after the repression of the Paris Commune, revolt tended towards the individual act of violence, often directed towards kings, politicians, soldiers, police officers, tyrants, and magistrates. Numerous militant anarchists were imprisoned and faced the guillotine. Men such as Ravachol, considered by many to be terrorists, were condemned to death.