The Union officer known for his defense of Little Round Top was Joshua Chamberlain.

As the commanding officer of the 20th Maine Regiment, Chamberlain was instrumental on July 2, 1863, during the Battle of Gettysburg. His troops defended the far left flank of the Union line against several Confederate attacks. In a remarkable display of courage, he commanded a bold bayonet charge when his men were running low on ammunition, successfully driving back the enemy. Chamberlain's leadership and valor at Little Round Top were crucial in preserving the Union's defensive stance throughout the battle.