Captain Thomas Benton Weir (September 28, 1838 – 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.

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.

[2] During the Indian Wars on the Great Plains, Weir commanded Company D of the 7th Cavalry under Custer, as part of a two-pronged attack on a large Native American encampment on the Little Bighorn River in Montana on June 25, 1876.

However, Weir and the would-be relief were forced to retreat back to Reno Hill under fire where they were under further attack until relieved by General Alfred Terry two days later, when the Native American warriors withdrew.

[5] Deeply shaken by his experience after the famous battle and showing symptoms of post-traumatic stress, Weir's mental health declined rapidly.

[6] Formally posted back to New York City on recruiting duty, in the final months of his life he refused to go outside, began to drink heavily and in his last days was said to be extremely nervous, to the point of being unable to swallow.