Principal People Involved in the Dreyfus Affair:

George Clemenceau (1841-1929) was a journalist, politician, and leading Dreyfussard. He was the Political editor for the newspaper, L'Aurore, and chose the name, J'Accuse, for Emile Zola's controversial open letter to the president of the Republic. Clemenceau himself actually wrote articles protesting Dreyfus's unfair conviction and imprisonment.

Edgar Demange (1841-1925) represented Mathieu Dreyfus in the Esterhazy trial, and was Dreyfus's co-defense attorney with Labori at the Rennes trial. Though both Demange and Labori staunchly supported Dreyfus, they had opposing strategies on how the representation should be conducted.

Captain Alfred Dreyfus (1859-1935) was serving a Jewish General Staff officer in 1894 when he was falsely accused of high treason for allegedly telling French military secrets to the Germans. Dreyfus was convicted on shaky evidence, then sent to Devil's Island as punishment. His case was retried in 1899, but he was reconvicted. Ultimately, the President of the republic offered him a pardon, which he accepted reluctantly on the condition that he could continue trying to prove his innocence. In 1906, Dreyfus was finally rehabilitated.

Lucie Dreyfus was the wife of Alfred Dreyfus. She worked closely with her husband's defense counsels. She was instrumental in Dreyfus's retrial in 1998, and his rehabilitation in 1906.
Further Reading

Mathieu Dreyfus was the brother of Alfred Dreyfus. Mathieu was the principal organizer of the Dreyfussard campaign, responsible for recruiting Dreyfus devotees such as Edgar Damange, Bernard Lazare, etc.

Armande Mercier Du Paty De Clam (1853-1916), known to be somewhat bizarre, was the General Staff officer who arrested Dreyfus and conducted Dreyfus's prison interrogation. Armande Mercier Du Paty De Clam was the first to declare that the bordereau was in Dreyfus's hands, and testified against Dreyfus at his trial. Armande Mercier Du Paty De Clam, in cahoots with Colonel Henry, also compiled the fraudulent "secret dossier," designed to help protect Esterhazy.

Comamdant Ferdinand Walsin-Esterhazy (1847-1923) was a French infantry known to be gambler, debtor, and a womanizer who married into the aristocracy. Esterhazy spied for the German attaché in Paris, and Dreyfus was ultimately accused and convicted for Esterhazy's treason. He was protected by Armande Mercier Du Paty De Clam and Colonel Henry. Esterhazy was court martialed in 1898 and was acquitted. After Colonel Henry confessed to forging decisive documents in the Dreyfus case and committed suicide, Esterhazy fled to England and remained there until his death.
Further Reading

Felix Faure (1841-1899) was an anti-Dreyfussard who was the sixth President of the Third Republic.

Commandant Hubert-Joseph Henry was an officer in the army's statistical section who was later promoted to head of the intelligence office. He conspired with Armande Mercier Du Paty De Clam to frame Dreyfus, and forged numerous documents ("secret dossier") to achieve that end. He was arrested in 1898 and committed suicide while he was in prison.

Jean Jaures (1859-1914) was the leading socialist in the Chamber of Deputies, historian, and journalist. Ultimately he convinced his party to support a review of the Dreyfus case.

Bernard Lazare (1865-1903) was one of Dreyfus's earliest supporters who devoted much writing to advocating Dreyfus's innocence.

General Auguste Mercier (1833-1921) was the Minister of War who was responsible for Dreyfus's first arrest in 1894 and testified at every major trial.
Further Reading

Lieutenant Colonel Georges Picquart (1854-1914) was one of the foremost Dreyfusards. He was promoted to chief of the Statistical Section in 1895. When he discovered Esterhazy's treason, he tried to convince the other members of the General Staff of Dreyfus's innocence. He was imprisoned in 1898, and was dismissed from the army. He was reinstated in 1906 and was promoted to General.
Further Reading

Emile Zola (1840-1902) was another of the formost Dreyfusards. He was a well-known French novelist, who became a chief advocate of Dreyfus's innocence. He wrote many articles defending Dreyfus, the most well known being his letter to the President of the French Republic entitled J'Accuse.