The hero of the Revolutionary War who became a traitor when he decided to help the British was Benedict Arnold.
Explanation:
1. Benedict Arnold was initially a respected American general who played a crucial role in the early stages of the American Revolutionary War.
2. However, he later conspired with the British to surrender the fort at West Point in exchange for money and a high-ranking position in the British army. This act of betrayal made him infamous in American history.
3. Benedict Arnold's name has since become synonymous with betrayal and treason due to his actions during the Revolutionary War.
