Arnold, Benedict (1741-1801), American military leader, who distinguished himself early in the American Revolution (1775-1783) but later betrayed the American cause. Arnold was born in Norwich, Connecticut. As a militia colonel, he helped take Fort Ticonderoga in New York from the British in 1775. In 1776 his delaying tactics on Lake Champlain thwarted an enemy drive to New York City, which would have divided the colonies. In 1777 he distinguished himself in the Battle of Ridgefield, Connecticut, and during the Saratoga campaigns in New York.
In 1778 Arnold became commander of Philadelphia, where he squandered money on an extravagant social life. In 1780 he agreed to surrender the fort of West Point to the British in return for payment and a royal commission in the British Army. The plot was exposed, and Arnold fled to the enemy. Arnold then led attacks on the colonists and advised British officials on the conduct of the war. Following the war, the British excluded the distrusted traitor from active military service, and he received less than one-third the money he had sought.