Orrin Porter Rockwell- American Frontiersman and Early West Gunfighter

Porter Rockwell killed more outlaws than Wyatt Earp, Doc Holladay, Tom Horn, and Bat Masterson combined, earning him the menacing title, the “Destroying Angel.”

Rockwell’s hawk-like vision was so acute he could spot landmarks along the trail days before his fellow pioneers. His accuracy was so deadly he once shot a bank robber attempting to escape on horseback in the pitch-black of night. It didn’t take long for Rockwell’s legendary abilities to draw the attention, and sometimes even the competition, of outlaws all throughout the Wild West.

http://www.ldsliving.com/Porter-Rockwell-7-Unbelievable-Facts-and-Stories- You-Didn-t-Know/s/77142

There are a number of well crafted biographies on "Old Port." Take a look at the Wikipedia page for him at the references.

Porter Rockwell is a well known family friend to the Taylors in their northern Utah Territory settlement. Myscal Taylor in "Arise from the Dust" learned pointers about six shot placement from the old gunfighter in the 1850s. While at Camp Tippecanoe, he was detailed to teach two young officers in the 20th Indiana how to aim their service pistols accurately. Both men were at Gettysburg on the 2nd day with Ward's Brigade on Houck's Ridge. A small distance across the small valley in front of Little Round Top. The officers have frequent nightmares about poorly aimed pistol shots and getting skewered by Rebel bayonets...

"Ah Taylor, there ye be looking like an old man before his time."

Myscal turned to see Corporal Martin standing behind him, hands on his hips. It seemed uncanny really, the man's ability to materialize at the oddest moments. The Corporal’s eerie knack to discern the content of his thoughts.

"What they got ye doing this time?" asked Martin with a curious glint on his lined face.

"They want a gratis pistol shooting lesson."

"Knowing somthin' about the subject?" reflected Martin

"Some. Been around pistols most of my life. Know my way around six-shooters," said Myscal.

"Ran into that Mormon gunman Porter Rockwell a few times around Camp Floyd," said Martin conversationally. “Also, stayed one night during a drivin’ snow storm at his tavern over by Point of the Mountain. Lord, he was somethin'. Wouldn't want to go agin’ him in a pistol fight. The glare in his eye, his long black and silver hair tumblin' down his shoulders─jes listenin' to his yarns was enough to frighten the starch out of me."

"Honestly? You don't seem like the kind to take the big scare easy," said Myscal truthfully, eyeing the Corporal.

"Nope, I'm not. But Lord, jes the look on that man's face when some fool asked him whether or not he done shot Governor Boggs of Missouri. He jes stared that man down. Gave me the boogermans. Took the chilblains out o’ the air a few minutes later when someone else asked him to tell the story of killin' Frank Worrell in '45."

Orrin Porter Rockwell made a lot of people nervous.

… Myscal returned from his recollections on Rockwell back to the present moment’s conversation with Corporal Martin. "Yes, he can put the grizzly scare into those that do not know him. He is a mighty generous man to his friends."

"Ye one of his friends?" asked Martin curiously, intrigued.

"He's a good friend of my father and uncle. He's bought a few horses off me. He taught me a few things about pistol shooting. It came in handy a few times."

"Now ain't ye a surprise! Knowin’ old Port Rockwell and all," grinned Martin with expressed delight. "They jes didn't know what a heller they brought into the army, now did they?"