Colonel Dyer is an officer stationed inside the Empire's shield generator bunker on Endor. When a Rebel strike team led by Han Solo and Princess Leia infiltrates the bunker to blow it up so the Rebel Alliance can destroy the second Death Star, they enter the control room, holding several Imperial technicians at gunpoint.
What they don't know is it's a trap laid by Emperor Palpatine himself. Waiting outside, Threepio, Artoo and Wicket the Ewok watch in surprise and horror as a gaggle of Stormtroopers, led by our man Dyer here, rush into the bunker. Just as the strike team is finishing up planting their explosive charges, the bad guys rush in. Dyer gets a little ahead of himself and his own subordinates, appearing, alone, to attempt to apprehend the Rebels.
"Freeze!" he yells, aiming his blaster pistol at them.
Han responds to this by grabbing an explosive charge that hasn't been primed yet and flinging it at Dyer.
Struck in the chest, Dyer lets out a cry that amounts to "Aaahhhh-hooooooooo!" and backflips over the safety railing behind him and plummets to his death in the generator's reactor core. But this tiny victory over one overeager officer is for naught, as our heroes are apprehended anyway when the rest of the Imperials get inside.