Alexander Keith McClung (June 14, 1811 – March 23, 1855) was an attorney from Vicksburg, Mississippi, U.S. marshal for the Northern District of Mississippi, a lieutenant colonel of the Mississippi Rifles during the Mexican-American War, and briefly chargé d'affaires to Bolivia in President Zachary Taylor's administration. He is best known today for his participation in a series of antebellum duels, or gunfights. He became a folkloric figure of the 19th-century United States, a dead shot with mental health problems known as "the Black Knight of the South," with claims made to the effect that he killed 18 people, or participated in 14 duels and had killed 10 men, or killed seven brothers in one family. (The historical record suggests four duels with two killings. A New History of Mississippi states that by the end of his term as U.S. marshal he "had probably killed 10 men.")

Born the seventh child of a Kentucky judge and "the most brilliant" female scion of the Marshall political family, McClung moved to Mississippi in 1832, where he built a lonely, storied, troubled life. He considered himself "Death's Ramrod." Amongst his contemporaries, he was considered a courageous soldier, a passionate Whig (devoted to Henry Clay, and opposed to Andrew Jackson), an excellent writer, an excellent shot, sensitive, melancholic, Byronic, erratic, alcoholic, and eventually, insane. He died by self-inflicted gunshot in a Mississippi boarding house in 1855, leaving a Romantic poem as a suicide note.

McClung was born in Fauquier County, Virginia, and was the nephew of United States Chief Justice John Marshall. His father was William Alexander McClung, and his mother was Sarah Tarleton Marshall. Judge McClung was a Virginia native, related to the Breckinridges, who represented Kentucky in the Virginia legislature, represented Nelson County in the Kentucky Senate from 1796 to 1800, and attended the Constitutional Convention that met in Danville, Kentucky, in 1787. Sarah Marshall was remembered as the "brilliant daughter of distinguished Revolutionary War veteran Col. Thomas Marshall...Susan was carrying her seventh child when she left her Mason County home in 1811 to visit a gravely ill sister in Virginia. That memorable year witnessed the birth of a son, Alexander Keith, on June 14th in the Old Dominion, and the death of her husband on their Kentucky estate that same summer." Several of McClung's siblings died young.

At age 14, he was sent to a "classical school conducted in Woodford Co., Ky., by his uncle, Dr. Louis Marshall. To escape punishment he leaped from a second-story window and fled to his home in Mason County. He attended the New York Naval Academy, where he once threatened fellow student Benjamin F. Sands at sword point. He was commissioned as a midshipman on April 1, 1828. He set sail on the USS Vandalia (1828) on October 15, 1828, and promptly showed further evidence of behavioral issues, getting into a fight with fellow midshipman J. T. Williams. At the port of Montevideo, Uruguay, his first duel was with midshipman Addison C. Hinton, later of the Republic of Texas Navy. Hinton wounded McClung in the arm, McClung nicked Hinton's thumb. McClung's naval career ended August 20, 1829, when his captain put him ashore in Buenos Aires, Argentina. Upon returning to Kentucky, he initially studied medicine but then turned to the law. His second duel was in Frankfort, Kentucky, opposite his cousin James W. Marshall; he fired into the air, concluding the matter of honor. There may or may not have been another shooting in here somewhere. A Marshall cousin wrote in the 1880s, "I know little of the circumstances under which he killed Baker." The McClungs deny the claim that he killed a man named Baker.

McClung moved first to Columbus, in northeastern Mississippi, in about 1832. He began working as a "not too successful" attorney but regardless of his lawyering skill he still managed to move within the circle of the state's most prominent politicians. Regarding his legal career, "A Mississippian" writing in the Southern Literary Messenger in 1855 commented, "notwithstanding his acknowledged talents and decided professional acumen, we have not been able to learn that he took any prominent stand at the bar, or transacted any considerable amount of professional business." Moving further south in 1833, in short order he served as "second" to Henry S. Foote in a duel with Sergeant S. Prentiss. At this duel, one of the typically baroque Southern duel cycles of gossip, rumor, slander, and melodrama was kicked off, in this case involving one Gen. Allen and a man named George W. Coffee. Thus, on July 14, 1834, McClung dueled and killed Mississippi state legislator Augustus Albert Allen. The duel was on the banks of the Pearl River, and McClung shot Allen in the mouth from 34 feet (10 m). McClung's shot amputated Allen's tongue and smashed "several teeth...leaving a horrific wound from which he died in great agony." As many as 3,000 people were present at the Jackson duelling grounds to witness this event.

In 1837 there was supposed to be a fight between McClung and H. C. Stewart, with the weapons being 16 in (41 cm) knives but McClung "absolutely refused to agree to the binding of their respective left arms with cords. Gentlemen, he contended, did not bind themselves like slaves and criminals. While the duel never took place, the barbaric terms were circulated in the Northern press as yet another example of Southern savagery."

McClung killed 24-year-old John L. Menefee in 1838. Menefee's first name is variously listed as George, James, and John W., and the family spelling was Menefee although the press generally used Menifee. He was a Vicksburg merchant, and he was the brother of Kentucky congressman Richard H. Menefee, and he was killed on "the second fire" of a duel with Mississippi rifles in Vicksburg in December 1838. The lead-up to the Menefee shooting involved Menefee and George Coffee ("McClung's old enemy") finding the completely inebriated McClung alone and unarmed in a tavern and "savagely beating" him with a pool cue to the point that they fractured his skull. This action led to the duel. As many as 700 people had ridden over to DeSoto Island, the "duelling island" across from Vicksburg, in boats to witness the shootout. Menefee was not killed directly by a bullet, but rather McClung's bullet hit the body of Menefee's gun and either a fragment of the hammer or half of the bullet entered above his right eye, or he was killed when a wooden splinter of the rifle stock cut through his neck. The crowd was against McClung, as Menefee was personally popular, and "the callous sporting crowd had reportedly bet heavily against McClung," since Menefee was a member of the local militia and was known for his excellent shooting skills. Menefee's unit, the Vicksburg Rifles, had all come to the dueling grounds to have a picnic and watch. Nearly 50 years later, in 1886, Menefee was still remembered by a Vicksburg booster as "one of the most brilliant and popular men in the State." After Menefee's death, other Menefees reportedly sought out McClung and he "fought seven of them killing three of the number and wounding the balance." Another version has it that, "As an aftermath, he was forced to methodically slay all six of his victim's brothers, one by one, in the order which they challenged him. One perfectly good family, 'shot to hell'—literally." The McClung family history claimed that his "formidable reputation saved him from ever again being challenged.

Writing in December 1854, "A Mississippian" described McClung's history of dueling: