Who ambushed Custer?

Actually, Custer was not ambushed at Little Big Horn. He purposely attacked a large Lakota/Cheyenne war camp led by Sitting Bull. Custer attacked hastily, against the advice of his scouts, afraid the camp would break apart and run before he could decisively engage them. Sitting Bull was not at the battle where Custer was killed. The ambush was lead by Crazy Horse.