St. Dennis (Denis) lived around 200AD. He was born and raised in Italy, and latter was sent as a missionary to Gaul, which is now France.
Denis was stationed at an island in the Seine, which became his missionary base. He became the first bishop of Paris as well as an Apostle of France. At some point, he was captured by Parisians, along with fellow saints Rusticus and Eleutherius.
Following a long imprisonment, Denis was beheaded and his body was thrown into the river. His converts retrieved his body and provided him with a proper burial. A chapel was eventually built over his tomb and this became the Abbey of Saint Denis.
St. Denis is the patron saint of Paris, France as well as those who suffer from headaches, frenzy, hydrophobia, rabies and the possessed. His day of feast is October 9. He is commonly pictured with Rusticus and Eleutherius.