Professor Nathan Garrett was born in London and was the descendant of Sir Percy of Scandia, the heroic Black Knight of Arthurian legend, but he lacked his heroic nature. Garrett achieved international respect as a brilliant research scientist and inventor whose particular specialty was genetic manipulation. He earned his doctorate at Oxford University and later taught there as a professor. It may have been at Oxford that Garrett fell in with and joined colleagues who were political leftists, and became a radical communist: it is not known at what point in his life, Garrett became a spy for the People's Republic of China.
At some point Garrett visited the castle he had inherited, Garrett Castle, where Sir Percy of Scandia was buried. The spirit of Sir Percy appeared to Garrett and presented him with the opportunity to become a modern day Black Knight crusading against evil. Garrett saw the original Black Knight's enchanted Ebony Blade in a scabbard near the tomb of Sir Percy, but, being unworthy, was unsuccessful in drawing the sword. Hence Sir Percy did not make Garrett his successor as the Black Knight.
Garrett moved to the United States, where his sister had gone to live, and he became a naturalized American citizen. Garrett led a highly distinguished career, continuing his scientific research, but he also acted as the head of an espionage ring. Finally, he was captured by Henry Pym, the original Giant-Man, and charged with treason for delivering American government scientific secrets to agents of Communist China. In order to prevent Garrett from betraying them at his trial, the Communist Chinese intelligence agency saw that Garrett's bail was paid. Garrett then fled the United States, using a counterfeit passport.
Garrett hid in a Balkan kingdom, rented a castle and plotted his revenge. He was determined to make himself a match for Giant-Man. Inspired by his encounter with Sir Percy's ghost and by a statue of a winged horse that he saw in this European country, Garrett decided to devise for himself the costumed identity of a criminal Black Knight. Using his genius at genetic manipulation, Garrett artificially mutated the horse Elendil to give it wings enabling it to fly. He also devised highly advanced weaponry, much of which he built into a power lance, and an armored costume similar to the original Black Knights.
Garrett secretly returned to the United States and robbed an armored car in the guise of the Black Knight. Giant-Man and the Wasp confronted the Knight when he attempted to steal a state-of-the-art helicopter. Garrett subdued Giant-Man with bolos and powerful cables, and he unleashed his itch-ray on him. Giant-Man escpaed by shrinking to ant size and reunited with the Wasp. Unnerved for the humiliating defeat, he fled on Elendil and vowed revenge. The Black Knight was soon recruited by Baron Heinrich Zemo to serve as a member of his Masters of Evil. He intent was to prove his worthiness by kidnapping Princess Elena Stragosz of Ksavia, while she was with her father, Archduke Emil Stragoz, in New York City, attending a United Nations Security Council meeting. The Knight fought the honor guard and Spider-Man, but his high school classmate, Sally Avril, died in a car accident while she attempted to photograph the event, and Garrett escaped. He took Elena to the Chrysler Building, where he was protected by dozens of medieval-clad minions while he contacted Zemo to relay his success. Later, Spider-Man arrived and threw aside the Knight's lackeys, and chased him out of the building. Spider-Man angrily beat him until the Human Torch intervened. As Zemo ordered the collapse of a nearby wall, the heroes were distracted and the Knight was removed. Despite this, Zemo allowed the Knight to join his Masters of Evil.
Later, the Masters attacked New York City, spraying the Adhesive X on the populace, trying to lure the Avengers into a confrontation. But, they were defeated when Rick Jones and his Teen Brigade replaced it with an antidote developed by Paste-Pot Pete, who wanted parole with his cooperation. The Avengers defeated the Masters of Evil, the Knight proving no match for the Asgardian thunder god Thor. Even though Thor enjoyed riding Elendil, he knew the horse didn't belong to him, so he didn't claim ownership. The horse soon circled the state penitentiary where Garrett was held, and Garrett, using his equipment, escaped. He wanted revenge on the Avengers, and he attacked the Stark Industries plant in Long Island and held Harold "Happy" Hogan hostage, in order to attract Iron Man; still, the Knight was defeated and brought to prison.
In prison, he and the Melter were allowed to wear their armors for a demonstration to a scientific delegation from Washington. But before that could happen, the Enchantress and the Executioner freed them so they could re-join the Masters of Evil. Their battle with the Avengers resulted in Zemo's apparent death and the Masters were returned to prison. Escaping again, Garrett was among the many super-villains manipulated by Doctor Doom via his Emotion Charger into attacking the FF in the wedding of Reed Richards and Susan Storm. There he battled the Angel before Reed used his Sub-Atomic Time Displacer to return all the villains to the past, leaving them with no memory of the event.
Taking over a castle that had been relocated to the Potomac River in the Washington, D.C. area years earlier by an English baron who had died before moving in, the Black Knight plotted his revenge once again. He kidnapped Happy Hogan again from a hospital in DC, having sustained critical injuries from a battle between Iron Man and the Titanium Man. The Knight had left clues intentionally, and Iron Man went to the castle, where they battled. Garrett disrupted Iron Man's circuitry using an ionic energy blast, and he took him into the air with Elendil, intending to kill Stark by dropping him. Iron Man, however, grabbed the saddle's stirrup and used his strength to unhorse Garrett. As both men fell, Iron Man landed in the river, but the Knight crashed into trees. Mortally wounded, he went to a nearby farmhouse and phoned Dane Whitman, his nephew, Arriving there, Garrett told him he regretted the choices he had made and he also told him he should use his research for good, not evil. Whitman agreed and Garrett died. Whitman inherited the Garrett Castle and the Black Knight mantle, becoming a hero, joining the Avengers and receiving approval from the spirit of Sir Percy. Garrrett's equipment and Elendil were later taken by Dreadknight.
Time later, an apparent Black Knight was used by Immortus in his Legion of the Unliving against the Avengers West Coast. In the battle, the Knight fell from his horse while fighting Hank Pym, apparently dying. Also, the Grim Reaper created his Legion of the Unliving, making an alliance with the Great Old Ones, and claiming to have used souls of deceased Avengers foes, including Garrett's, to animate corpses in order to attack the Avengers. However, it's not known if this was the true Garrett.
Scientific Ability: Nathan Garrett was a brilliant research scientist whose principal achievements lay in the area of genetics and engineering. His knowledge of various forms of advanced technology was sufficient to enable him to design and construct the weaponry he wielded as the Black Knight.
Body Armor: The Black Knight wore a lightweight full-body suit of electrically-insulated steel-alloy chainmail that protected him from projectiles like 45-caliber bullets at close range; however, it didn't protect him from a long fall. Also, his helmet visor could emit a bright light to blind foes temporarily. The suit weighed about 60 pounds.
Flying Horse: The Black Knight rode a black stallion, which he gave wings and power of flight through genetic engineering. The horse was able to lift aloft about 270 pounds beyond its own weight, and could fly at a top speed about 50 miles per hour for up to one hour before needing to rest.
Power Lance: The Black Knight's principal weapon was his atomic-powered Power Lance, which was rigged with a number of offensive technological devices.
Thermal Beam: The lance could emit an acetylene-based heat beam intense enough to melt through a two-foot thick steel wall at fifty feet within seconds.
Ionic Energy Blast: The lance could emit powerful electrical charges that could disable electronics. 
Force Blast: The lance could project electro-magnetic concussive beams of charged alpha particles exerting a concussive force sufficient to blast through a foot-thick wall of cinderblocks at fifty feet in four seconds. The maximum effective range of the power blaster was about 100 feet.
Bolo Cables: The lance contained two spools of eight-inch thick' conductive steel cable, fifty feet in length, which the Knight sometimes attached to bolo bells. The firing mechanism was a linear accelerator (magnetic cannon), which shot the cable through the lance, Especially when connected to bolo balls, the ends of the cable were weighted in such a way that the cable tended to wrap around a person or object like a bolo.
Machine Gun: On at least one occassion, the Knight concealed a .45 caliber machine gun within has lance.
Buzz Discs: The Knight could use the lance to fire red-hot spinning metal discs as weapons.
Sappers: The Knight could use the lance to fire super-heated metal "doughnuts" which affixed themselves to objects and drained electrical energy from them.
Paralyzer Pistol: The Black Knight also carried a "paralyzer pistol" that emitted a highly concentrated, fast-acting nerve gas capable of rendering an average human being unconscious in two seconds for one hour in small doses. A sufficient dose of the nerve gas could kill a human being through paralysis of the respiratory system.
This character appears in TSR Inc.'s RPG adventure The Weird, Weird West. In the plot, he had been hired by Doctor Doom in 1968 to travel back in time to 1871Dodge City. Alongside with other super-villains (including Sandman, Scorpion and Mysterio), he was to provide support to Doom while he analysed a time anomaly and tried to obtain profit from it. Doom took his lackeys (no name was provided for the team) to a Krozzar camp to deal with the Krozzars. Doom eventually found the origin of the anomaly, a chronovore, but he and his lackeys were also found by time-travelling heroes from 1989, and defeated.