December 9, 1876) was an officer in the 7th Cavalry Regiment (United States), notable for his participation in the Battle of the Little Bighorn, also known as Custer's Last Stand.
Weir served under General George Armstrong Custer during the American Civil War, and after the war continued serving under his command up to the famous battle in 1876.
During the Little Bighorn Battle, Weir disobeyed orders to remain in a defensive position at Reno Hill and led a cavalry group that attempted to come to Custer's aid.
Weir and the group retreated back to Reno Hill in the face of overwhelming numbers of Native American warriors.
A hill on the battlefield, Weir Point, is named in his honor and marks the farthest point of Weir's advance.
Reportedly deeply depressed by his experience in the historic battle, Weir's health declined, and he died only a few months afterwards, aged 38.