George Armstrong Custer.
Custer finished 34th out of 34 in the West Point class of 1862. He accumulated over 700 demerits while at West Point. He should have been assigned to some Podunk outpost but the Civil War meant a need for junior officers. Custer performed decently during the Civil War.
After the war, Custer engaged in numerous battles with Native American tribes, most infamously with the Cheyenne who were slaughtered at the Washita River.
Custer led an expedition that discovered gold in the Black Hills, leading to the Black Hills gold rush that infuriated the Lakota Sioux who considered the Black Hills to be sacred lands. Because the Sioux refused to sell the Black Hills land and defended it against gold miners, the US government decided to round up all the Plains Indians. Custer led the attack on a very large village with several thousand warriors from multiple tribes including the Sioux and Cheyenne. This despite being badly outnumbered. Custer and 260 of his men were killed.
Alas, because of Custer’s widow, Custer achieved a kind of hero status and generated more hatred for the Sioux who killed the “boy general”. Hollywood bestowed that status with movies like “They Died With Their Boots On”. Not until the 1970s or so was Custer treated with the kind of contempt he deserved.