Private Daniel Jackson was an American left-handed sniper from West Fork, Tennessee serving in the 2nd Rangers Battalion of the United States Army. He was one of the men selected by Captain John H. Miller to search for Private James Francis Ryan, during World War Two in the film, Saving Private Ryan.
He was a designated sniper, armed with a M1903A4 Springfield Rifle. An outstanding marksman, Captain Miller put faith in him on D-Day to secure the beach and watched when he killed another German sniper nearly 450 yards away from his position. He could also reload and fire again in just a few seconds, with most of his shots finding their target.
Apparently from the southern U.S., he appears to be a devout Christian, quoting scripture from the Bible while applying his skills in combat. He dosen't appear to be a good reader as shown when he mistakes another paratrooper's name for Ryan's.
D-Day on Omaha Beach
During D-Day, Jackson kissed his rosary bead while preparing to land. He managed to make it to the beachhead, waiting for his fellow soldiers to arrive. He then pushed up to a machine gun nest, proceeding to kill the gunner and destroy the position. Jackson later shot several Germans in the trenches with his sidearm.
He was chosen by Captain Miller to be part of a squad to find Private James Francis Ryan. While hiking to Neuville, he professed that God made him "a fine instrument of warfare", bragging that he could kill Adolf Hitler from up to a mile away.
Once in Neuville, he patrolled with 101st Airborne paratroopers. He overheard Private Adrian Caparzo lie to Corporal Upham about knowing everything about Miller, prompting Jackson to advise Upham to "watch for the bullshit". When trying to help a French family, Jackson engaged in a brief sniper duel with a German sniper, succeeding in shooting the soldier through his own scope. He later threatened to kill a group of German soldiers, wanting them to put their weapons down.
Jackson later fell straight to sleep in a church while the squad was resting, his squad mates discussing that he must fall asleep so easily due to having a "clear conscience".
When the squad reached a rally point, Jackson tried to give the wounded their hope that the 29th infantry would arrive soon. He was then ordered by Miller to search through a bag of dog tags, becoming frustrated at Reiben's complaining and quickly feeling ashamed for not considering the paratroopers watching them treat their friends tags as poker chips.
Once the group moved out, Jackson reached a radio site with the others. Miller wanted to engage but Jackson, with Reiben, tried to dissuade the captain, saying they had already abandoned German controlled 88s so why not leave the machine gun nest. Miller was adamant, however, so Jackson went along with it as did the others, even volunteering to charge up the left flank on his own. After the skirmish, Jackson and the others tried to save a mortally wounded Medic Irwin Wade but failed. Angered, he heavily beat Wade's killer along with Reiben and Private Stanley Mellish, even prepared to execute him had Miller not intervened. He later prevented Corporal Upham from handing the prisoner a drink while they forced the man to dig a grave. Jackson waited eagerly to kill the man after the graves were dug but never succeeded as Miller let them go. This led the group to argue heavily with each other, Jackson drawing his gun on Sergeant Horvath, the hostility only ending when Miller confessed his life before the war to them all.
Ramelle and death
While at Ramelle, Jackson was stationed in the bell tower, acting as a scout and a sniper with assistance from Private Parker. He made a sticky bomb out of his socks to help the others disable the incoming tanks. He passed the time before the skirmish by scouting for any incoming infantry. When the Germams did appear, he relayed the strategy of the resistance and quickly began to engage the Germans. Despite successfully killing at least a dozen German infantry, Jackson met his demise when a Tiger Tank fired a shell at the tower, decimating Jackson and Parker.
While he implements his faith into his talents, he quotes from the "King James Version" of the Bible.
Psalm 22:19 - Spoken while killing German machine gunners in Omaha Beach:
But be not thou far from me, O my strength, haste thee to help me. 
Psalm 25:2 - Prayed while killing the German sniper in Neuville:
O my God, I trust in thee: let me not be ashamed, let not mine enemies triumph over me. 
Psalm 144:1-2 - Spoken while killing several German soldiers in Ramelle:
Blessed be the Lord my strength which teacheth my hands to war, and my fingers to fight: My goodness, and my fortress; my high tower, and my deliverer; my shield, and he in whom I trust; who subdueth my people under me. 
The scene where Jackson kills the enemy sniper through their own rifle scope was actually accomplished by a real life Marine sniper named Carlos Hathcock. Nicknamed the "White Feather" by the North Vietnamese army, he was best known for the infamous Scope shot. As well as eliminating a Viet Cong platoon leader named "Apache" who had a reputation for capturing and torturing U.S. Marines. The PAVN (People's Army of Vietnam) had placed several bounties on Hathcock's head, which numerous soldiers tried to collect. Most notably, a Vietnamese sniper by the name of the "Cobra". During a showdown at Hill 55 located in Vietnam, Hathcock saw a glint from the Cobra's rifle scope and fired at it, the round had traveled through the scope and into the sniper's eye.