Kro is a warlord, dictator, and general to the Deviants; Deviants being an offshoot of the evolutionary process that created human life on Earth instigated by the Celestials. They were created to wage war against their counterparts, the Eternals. He is more than 100,000 years old and secretly an immortal-shapeshifter closer to the Eternals then his own kind, forcing him to hide his powers from his people. Over the centuries he has been mistaken to be the Olympian Pluto, the Devil, and many other mythological figures. He is the secret lover of Thena and because of this has sometimes been a reluctant ally of the Eternals.
Kro was born in Lemuria to the race of Deviants, an evolutionary offshoot of humanity, cursed with an unstable genetic code causing random physical characteristics to crop up in each newborn child in the race. Kro was born with a number of traits which appeared to be unique among the Deviant race and which were beneficial in nature. Chief among these mutations were those granting Kro his longevity and near-indestructibility, both similar to those of another evolutionary offshoot of humanity, the Eternals.
Across the Ages
Kro carefully guarded the secret of his longevity by assuming a series of different identities among the Deviants over the course of his extraordinarily long life, using his powers to alter his facial features to complete his disguises. Kro feared that if he allowed the other Deviants to know that he was virtually immortal, they would subject him to genetic experimentation in order to learn how to duplicate the mutations that gave him his near-immortality in themselves. Kro studied the arts of warfare throughout his life and often led Deviant armies in his various guises. Across the centuries he was confused for various mythological figures such as the Olympian "Pluto", the Devil, and Satan, occasionally growing horns to match these roles.
5th century B.C.
In Babylon 2,500 years ago, Kro met and fell in love with Thena, daughter of Zuras, ruler of the Eternals of Earth. Thena returned Kro's love, but their relationship, perhaps the first such liaison between the two divergent races of humanity which had long been enemies, ended badly. Kro and Thena parted, although they retained strong feelings for each other. Thena assumed that Kro eventually died, and was surprised when she encountered him again in recent years. Kro attempted to renew their relationship, but failed.
Kro had many interactions with normal humans, usually sowing chaos wherever he went. Adopting a devilish appearance, he was believed to be Pluto, Satan, and other underworld rulers - Kro did not dissuade these cases of mistaken identities. He was constantly thwarted by the Eternal known as Makkari, first mistaken as the god Mercury then in his assumed identity as Hurricane.
The first such clash, Kro assumed the guise of Prussland dictator Rudolph Hendler, sparking war across Europe. However, Makkari (as Mercury) thwarted this plan by preventing the warring armies from continuing their conflict, eventually lulling them into peace, and forcing Kro to flee. Fleeing to America, and continuing to use his Pluto guise, Kro attempted to destabilize whatever human society whenever possible.
Assuming the alias Paul Sayden, Kro set up operations in Coast City, facilitating the criminal activities of Piggy Perroni. This operation was foiled by Makkari (operating in his Hurricane identity), and Pluto ultimately fled after losing a battle against Hurricane at a costumed party. Relocating to the Mato Grosso region of Brazil, Kro unleashed the deadly "Green Plague" in the region. He then allied himself with Jivaro headhunters, convincing them to kill anyone who attempted to cure the disease. This plot was also foiled by Hurricane, although Kro was long gone by the time a cure for the disease was discovered.
In his last recorded appearance while operating as Pluto, Kro returned to America, setting up in Groton City under the alias "Mr. S Devile". There he hired mobster Scarface Rispoli and had him place "Death Boxes" in subways to cause fatal accidents that would slaughter all passengers aboard. This plot was once again foiled by Hurricane who captured Rispoli and prevented Kro from planting yet another Death Box. Overpowering Kro in battle, Hurricane sent him fleeing into the sky.
In the early 1970s, Kro and Thena met again during the Vietnam War. Their reunion resulted in Thena becoming pregnant with twins. She used advanced Eternal technology to transplant them into the womb of an infetile human woman named Mrs. Ritter who gave birth to them and raised them as her own twin children, Donald and Deborah.
When the fourth Host of the Celestials was approaching Earth, Kro was ordered by Brother Tode, the monarch of the Deviants, to find and disable the Celestials' cosmic beacon. After he failed, he was tortured by Tode. To save himself, Kro proposed taking the form of the humans' devil and attacking New York City in order to trick the humans into attacking the Celestials. He managed to capture Ikaris, who was defending the city, and entombed him in a capsule at the bottom of the ocean, along with Sersi and Margo Damian. Convinced that humanity would be driven to aggression against the Celestials, he agreed to a truce with Thena and allowed the existence of the two races to be revealed to Professor Samuel Holden and his students.
Invasion on Olympia
After the demise of Zuras, Brother Tode led an assault on Olympia, the principal city of the Eternals, where the Deviants captured and imprisoned all the Eternals. Almost the entire Deviant ruling elite, including Warlord Kro, accompanied Tode and Deviant troops on this venture. Thanks to the intervention of James Rhodes as Iron Man, the Eternals regained their freedom and captured the Deviants that were on Olympia. The Eternals decided to transform all of the captured Deviants into a large block of atoms and send the block into outer space. Before the Eternals carried out this plan, Thena secretly released Kro from his cell, and Kro escaped. Shortly thereafter, most of Earth's Eternals left for outer space. Thena became the ruler of the Eternals left on Earth.
Rivalry with Ghaur
Kro made his way back to the Deviants' city in undersea Lemuria, intent on making himself their monarch now that virtually the entire Deviant ruling class was no more. To his astonishment Kro discovered that the Deviant priesthood, headed by the priest lord Ghaur, was manoeuvring to become the true ruling power in Deviant Lemuria. Since one of the priesthood's roles was to designate the new monarch, Kro confronted Ghaur and made his wish to become king clear. Ghaur allowed Kro to become monarch, but continued to pursue his plans. He had Kro lead an expedition to the Pyramid of the Winds, an Eternal structure in the Arctic, to retrieve a mysterious vial. Ghaur apparently hoped that Kro would be killed by the Eternals in the course of this venture. Once Kro found the vial, a Deviant priest and his guards demanded he give it to them, but Kro, determined to maintain his authority as ruler, refused. A party of Eternals led by Ikaris arrived, and Ikaris fought Kro for the vial. Thena, still in love with Kro, prevented Ikaris from killing him, and, on Kro's request, teleported Kro away. The Deviant priest's guards had managed to get hold of the vial for their masters. Kro and Thena traveled together as renegades, each hunted by his or her own race. They were finally found by Ikaris, who let them go after he replaced Thena as Prime Eternal. However, Ghaur still sought to capture Kro. 
Kro watched Quasar battle Tutinax when trying to save Ransak the Reject. Tutinax quickly took the upper hand as images of Quasar's father took the place of Tutinax, distracting Quasar, but was later beaten by Ransak.
The Herod Factor
Kro learned of Donald and Deborah's existence after a mutated Ajak began murdering twins across the US. Controlled by a vengeful Dr. Daniel Damian, the Ajak monster was searching for the "Chosen Ones," knowing their origin as Eternal-Deviant hybrids. Thena brought them to Olympia for their safety but the mutated Ajak pursued them there and captured them, then brought them Damian in Peru. Once the threat posed by Damien had been ended, Thena told the twins their origins and then took them to meet their father.
Kro later formed the Delta Force Deviants to help fellow Deviants. When the injured Eternal Sersi fell into Kro's subterranean hideout beneath the Pentagon and asked for assistance in rescuing the Avengers, Kro facilitated his Delta Network to gather the right Deviants for the rescue operation. When Maelstrom began attacking the Eternals, Kro took his human children away into hiding to protect them from the threat. ... While away with Delta Force, Kro and Ghaur divide grew causing factions the external world became concerned about and Wakanda came to the city to intervene. Kro continued on as the formal monarch.
Sometime later, the Deviant males were rendered sterile causing a power struggle between Ghaur and Ereshkigal. Ghaur usurped the position and promised his people he would fix their fertility problem with the help of the kidnapped Eternal; Phastos. Thor came to his rescue and took down Ghaur. Kro came to Ereshkigal with the activated the Unbinding Stone of Oshemar, but the power was to much to control and grew out of hand threatening reality itself. Thor was able to destroy the weapon but not before Ereshkigal and Ghaur disappeared. Kro used this opportunity to take control of the Deviants.
Despite his Deviant heritage, Kro possesses a number of superhuman traits characteristic of an Eternal:
- Regenerative Durability/Immortality/Toxic Immunity: Kro maintains a virtually unbreakable mental control over the processes and structure of his body even when he is asleep or unconscious. As a result, Kro has a lifespan that has already lasted over 20,000 years and is immune to disease and aging. His mental control over his body enables him to maintain a youthful, vigorous physical condition. Kro is not as nearly indestructible as the Eternals. (For example, Ikaris nearly killed Kro once by strangulation.) But while sufficient force can kill Kro, he can use his mental control over his body to heal himself after being injured.
- Malleability: Kro also possesses the power of physical malleability, which is atypical for a Deviant. At will he can cause most of the tissue of his body to become pliant, enabling him to shape it mentally like putty into different configurations. Once the tissue is set in an altered form, Kro has only to stop concentrating and his body will retain that shape until such time as he concentrates upon changing it again. This ability enables him to disguise himself and take the appearance of others (with cosmetic help for skin color, body hair, and so forth). One of Kro's favorite ploys is to pass himself off among ordinary humanity as a demon by fashioning horns on his head.
However, Kro's shape-changing powers are limited. He cannot alter the shape of his skeleton in more than minor ways. Moreover, he cannot eliminate any of his mass while transforming; he can only redistribute his 320 pounds of weight. Hence, he usually only uses his shape-changing power to alter his facial features. He can mentally mold the shape of his skull somewhat.
Kro has about three times the physical endurance of an ordinary human athlete. His heart is not located in the same place as an ordinary human being's; its true location is unrevealed.
Kro is a master military strategist, a superb military commander, a good hand-to-hand combatant, and an expert in the use of Deviant weaponry.
Kro frequently wears special glasses designed to extend his vision into the infrared and ultraviolet ranges. Hence, if Kro is wearing these glasses in a room where there is no visible light, he can still detect objects by perceiving the heat (infrared radiation) they give off.
Kro has employed a number of weapons developed by Deviant technology. Among his favourites are flame-guns, vibro-whips, and shroud-guns. Once while battling Ikaris, Kro wore gloves from whose fingertips he could project vastly powerful force blasts which could not injure his virtually invulnerable Eternal foe but instead caused Ikaris intense pain.
- The idea that Kro is over 100,000 years old was implied in Eternals (Vol. 5) #3 when the Machine showed its unseen audience an audio-visual recording of a conversation made at that time between Sersi and Thena in which a Deviant warlord named Kro who had been Thena's lover was mentioned. This date is problematic because, beginning with his entry in Official Handbook of the Marvel Universe (Vol. 2) #7, Kro has consistently been described as having been alive for 20,000 years. Subsequent issues have supported the far shorter lifespan, with Kro telling Sersi that he had lived for twenty thousand years and the Machine's narration stating that Kro had known Thena for nearly twenty thousand years.
- Kro (Earth-616) on Wikipedia.org
- Marvel Universe Vol 1, No. 4–7 September-December 1998; Featuring: The Monster Hunters, Harvey Elder (pre Mole Man)
- All-New Official Handbook of the Marvel Universe A to Z: Update #3
- Red Raven Comics #1
- Marvel Universe #6
- Captain America Comics #1
- Captain America Comics #3
- Official Handbook of the Marvel Universe #6
- Eternals #1
- Eternals Vol 5 #3
- Official Handbook of the Marvel Universe A to Z #6
- Eternals: The Herod Factor #1
- Eternals #6
- Official Handbook of the Marvel Universe Vol 2 #7; Kro's entry
- Captain America: Forever Allies #4
- Captain America Comics #2
- Marvel Universe #4-#7
- Eternals #3
- Eternals #4
- Eternals #5
- Eternals #6-13
- Iron Man Annual #6
- Eternals Vol 2 #2-12
- Quasar #12
- Avengers #370-371
- Fantastic Four Unlimited #10
- Heroes for Hire #5-7
- Black Panther Vol 3 #27
- Thor: The Deviants Saga #2-5
- Eternals Vol 5 #8
- Eternals Vol 5 #9
- All-New Official Handbook of the Marvel Universe A to Z: Update #3
- Official Handbook of the Marvel Universe A to Z Vol 1 6