Which Union general was killed on the first day of the battle?

Union General John F. Reynolds was killed on the first day of the Battle of Gettysburg. He was shot while directing Union troops near Herbst's Woods west of Gettysburg on July 1, 1863.

Reynolds commanded the left wing of the Union Army of the Potomac, which included the I, III, and XI Corps. He rode forward to help organize the arriving troops and reportedly encouraged the Iron Brigade as it entered the fighting. A bullet struck him in the back of the head, killing him almost immediately.

His death was a major shock to the Union army. Although Reynolds was one of its most respected commanders, the Union position was stabilized during the day and later strengthened on Cemetery Hill and nearby heights. Major General Abner Doubleday temporarily succeeded him in command of the field's Union forces.

George Meade was the overall Union army commander, but he was not killed at Gettysburg. Joshua Chamberlain became famous for defending Little Round Top on the second day, and Winfield Scott Hancock commanded the Union center.