George Armstrong Custer was arguably one of the worst men ever to wear the uniform of an American Army officer. He got his head handed to him at the Battle of the Bighorn. And by every objective military standard he deserved to. It’s just a shame the men of the 7th. Cav. had to pay the price as well.
In reality, George Armstrong Custer was the finest Cavalry Officer that the US Army ever produced. The fact that he had the poor luck to be killed along with his men is what has allowed the survivors to heap all of the blame for the disaster on him, when in fact he was poorly served by a number of Officers in his command, and arguably, had they chosen to vigorously support Custer, the disaster at Little Big Horn might well have gone very differently.
And it was still Crazy Horse, not Sitting Bull, who led the attack on Custer.
On the other hand, he may have helped win the Civil War when his forces collided with Jeb Stuart's cavalry near Gettysburg, preventing them from hitting the back of the US line on Missionary Ridge at the same time Pickett's Charge was hitting the front.