What did Eli Whitney invent?

Eli Whitney invented the cotton gin. He was a pioneer in ushering in the interchangeable parts system, and he created milling machines that allowed workers to cut metallic parts for weapons.

Whitney invented the cotton gin on a plantation under the employ of Catherine Green, a widow of a general from the Revolutionary War. He created the gin in response to the extensive manual labor that was necessary to clean the seeds from green-seed cotton. The gin used a network of wires, rotating brushes and hooks to clean the cotton. The machine created more cotton in 60 minutes than many workers in an entire day. The machine became a hit among farmers, but a slew of legal battles followed as others tried to mimic Whitney's invention.