The correct answer to this open question is the following.
The warmongering European Emperor who was banished to Isola d’Elba off the coast of Tuscany in Italy and St. Helen's island in the South Atlantic was French former emperor Napoleon Bonaparte.
Once a so much respected emperor of France, after some hard defeats in 1812, Napoleon started to crumble. He was defeated by the Russians, by the Spaniards, and he was completely defeated in 1814 by the British.
Indeed, he was on exile in the Island of Elba for a while, but his tenacity made him to scape and returned to Frace for a "great come back." In order to accomplish that, he formed a new army but was crashed in Waterloo, in June 1815. He again was exiled, now on the Island of St. Helen, where he died in 1821.
