Tadeusz Kosciuszko was a Polish patriot who came to the Ameircan colonies to help the colonists in the Revolutionary War.
Kosciuszko was not really a fighting leader. Instead, he was skilled in military engineering. This meant that he had the sorts of knowledge and skills that were needed to help the Americans build defensive positions and use their artillery. His help was, for example, important in the American victory at Saratoga. Kosciuszko also built forts for the Americans, including the one at West Point, NY where the US Military Academy now is.
Kosciuszko was motivated by his ideals. He believed that people should have just and legitimate governments. These beliefs motivated him to become an important factor in the American Revolution.