Now to get things started:
HOW I WOULD INTRODUCE THE AGENTS OF ATLAS INTO THE MARVEL CINEMATIC UNIVERSE
As the movies have established, the Avengers Initiative existed before the formation of the actual team. As it turns out, it's much older than we were initially led to believe.
The Avengers Initiative was first created in the 1950s by SHIELD, then a fledging NATO task force formed from what was the wartime Strategic Scientific Reserve to track down, study, and contain HYDRA Tesseract technology that was still unaccounted for after the war, as a replacement for Captain America. Almost immediately after his disappearance, attempts to recreate the super soldier formula were made, but were up until that point fruitless. With the threat of HYDRA technology loose in the world and potentially falling into Soviet hands, as well as the looming shadow of communism and the propaganda war that needed to be waged against it, it was felt that a hero like Captain America to serve as both a field agent and a symbol was needed.
That need was answered when SHIELD agents encountered Marvel Boy, a teenager who had been raised and empowered by extraterrestrials who returned to Earth to get to know his home world. SHIELD recruited Marvel Boy as one of their agents, and set to work recruiting other unique individuals they had encountered in their search for HYDRA tech, and brought them together as their primary field team, the world's first super hero team, dubbed The Avengers.
This first Avengers team was tasked with retrieving Tesseract technology that had fallen into the hands of Russian and Chinese forces, and battling threats to global security and peace that arose from that technology. As secrecy was of the upmost importance during the Cold War, especially where weapons technology was concerned, the team's existence and activities were, initially, kept top secret, with plans to eventually reveal their existence to the public to be used as a weapon of propaganda against the Soviets after the threat of the HYDRA technology was dealt with.
The team consisted of:
Marvel Boy: Robert Grayson, a young man who's father, an engineer specializing in communications technology, made contact with a colony of Eternals living on the planet Uranus. The Eternals brought him and his infant son to Uranus as they were curious about modern humans and he was convinced that the impeding world war would mean the end of human life on Earth. There, their bodies were altered to be able to survive in Uranus' atmosphere, and young Robert, as he grew, was further altered to have a physiology similar to that of the Eternals. As their skills in bio-engineering were limited in comparison to the god-like Celestials that made them, his bio-augmentation was assisted by electronic implants, namely his Quantum wrist bands, which served as a catalyst for his body's internal energy reactions as well as a regulator, and his head band, which facilitated his psionic abilities. When he turned 17, having learned the war had been over for five years, he returned to Earth to see his home world.
Marvel boy possessed superhuman strength and durability, flight, the ability to generate an enormous amount of energy which he could direct outward as heat and light, telepathy, illusion casting, heightened intelligence, and a halted aging process. In addition to being one of the team's heavy hitters, he was also their chief scientific advisor. The space ship he traveled to Earth in also served as the team's transportation.
Venus: A mysterious woman found guarding a jewel necklace made from a Tesseract fuel cell in rural Italy. When questioned, she remained evasive about her origin, only occasionally claiming to be the actual Greco-Roman deity incarnate as a human, though these claims were all taken in jest. She possessed the ability to influence the minds of others, alter her physical appearance at will, and seemed to be unable to be killed by known conventional means. The working theory as to her nature by SHIELD scientists is that she had been in some way altered by exposure to Tesseract energy, which she would neither confirm nor deny.
Namora: A member of an amphibious species of intelligent primates that splintered off from a common ancestor to humanity ten million years ago who was first encountered by SHIELD during an operation to thwart Russian attempts to retrieve lost HYDRA aircraft from the ocean floor. Taken into SHIELD custody, she agreed to work as a field agent in exchange for her freedom but refused to share any information about her people. She possessed incredible strength, speed, and durability, as well as highly acute senses. She possessed a dolphin-like ability to echolocate, as well as an ability to reproduce a wide range of sounds, from ear splitting pitches to normal human speech. Due to having an over developed language center in her brain, she was also able to learn new languages extremely quickly. Like most sea mammals, she possessed enormous lung capacity, able to hold her breath for hours at a time, but unlike most sea mammals her species seemed to evolve organs capable of extracting oxygen from water, allowing her to breath under water as well as on land.
Gorilla Man: A highly intelligent Gorilla capable of human speech Captured by SHIELD after they received confirmed reports of such a creature existing in the congo. The ape claimed to be a human named Ken Hale, former Marine and big game hunter/mercenary living in Africa, who killed a supposedly magical ape and in turn inherited it's curse and became an ape himself. SHIELD could confirm the existence of a Marine named Kenneth Hale who's last known location was Africa, but could neither confirm not deny the creature's story. The more widely accepted theory is that it was a normal Gorilla that had in some way had it's intelligence enhanced, either through exposure to Tesseract technology or some other means, and in it's confusion adopted the life story of Kenneth Hale, who it presumably encountered, as it's own. They made it a point never to share this theory with him. Gorilla Man possessed all of the physical attributes of a Gorilla combined with the intelligence and personality of a trained soldier. She was a skilled marksman and fighter, and wielded a customized gun built for his fingers.
3D Man: Charles and Harold Chadler, two brothers fused together into a gestalt being with a shared consciousness after being exposed to alien technology. This new entity, dubbed 3D Man by SHIELD scientists, possessed three times the strength, speed, agility, and durability for a normal human, as well as the ability to see through illusions and recognize shapeshifters regardless of what form they took. The two brothers could separate, but while Hal would return to normal Charles would shift out of phase with this reality, so they were reluctant to do so. The combined 3D Man entity possessed a unique sense of self and perspective on reality, giving the impression to some people of constantly being under the influence of mind altering drugs. He sometimes had a hard time distinguishing between individuals and had a poor sense of personal space.
M-11: A robot created by an American scientist working under to under threat Chinese intelligence operatives using salvaged Tesseract technology. The scientist had a crisis of conscience and planned to betray the Chinese. In retaliation, they killed him, but not before he instilled in the robot a sense of self and human emotion, so that it might defy it's masters and not be used as a weapon. It wandered off on it's own, and was eventually discovered by SHIELD. M-11 possessed a rudimentary sense of self and emotions. It's capacity for complex thought was limited, almost child like, but it was capable of forming emotional attachments to others and developing a personal set of ethics. M-11 possessed superhuman strength, was covered in a thick armored shell that could withstand explosions, and could emit a deadly and destructive electro-static blast.
Jimmy Woo: Former FBI field agent recruited into SHIELD, he served as the team's handler and leader. A gifted tactician and criminal investigator with a strong desire to prove himself due to the glass ceiling he experienced in the FBI due to his race. No superhuman abilities, but skilled fighter and marksman.
Together, The Avengers had many adventures, including battling the legendary Russian assassin The Winter Soldier, a race of shapeshifting aliens drawn to Earth by tesseract energy signals known as The Skrulls (including one posing as Senator Richard Nixon), and the giant draconic alien Fin Fang Foom. Their greatest and most frequent enemy was Pan Tzu, AKA The Golden Claw, a Chinese intelligence operative with ties to the Atlas Foundation crime syndicate who served as their counterpart on the other side. Intelligent, ruthless, and with strong connections in both the Chinese and Russian governments and organized crime, Pan Tzu worked for the Chinese government to further his own ambitions of social engineering and moving the world towards order and away from chaos, and was a regular thorn in the team's side. He possessed a strange respect for their leader, Jimmy Woo, and saw his antagonizing him as a way of strengthening Woo into someone who might have a place of leadership in the world to come.
Unfortunately, all of this came to an end in a disasterous mission against a research facility run by Pan Tzu in 1958 which resulted in the deaths of Namora, Gorilla Man, and M-11. Considered a failure, the team was disbanded and knowledge of their existence was classified and buried.
The remaining members went their separate ways. Venus simply dissapeared, never to be heard from again. The 3D Man entity, distraught over the deaths of his teammates, retired to go on a quest for spiritual enlightenment. He ended up founding a religion in Los Angeles called the Trune Understanding in the lade 70s, and the Harold Chambers half of the entity died of a drug overdose on his house boat in 1980. Jimmy Woo remained as a member of SHIELD, eventually obtaining a high level administration position. Marvel Boy remained on as a SHIELD operative, but his Quantum Bands fell into disrepair due to simple wear and tear, especially after injuries sustained in the final battle against Pan Tzu. He went on a brief sabbatical to return to Uranus and have them repaired, but the Eternals, along with his father, had long since left the solar system, leaving no trace behind.
With his powers now severely depleted, Marvel Boy is no longer able to survive in Earth's atmosphere, and has to live in a special, environmentally controlled apartment that simulates Uranus' atmosphere. The only powers of his that remain are his telepathy, illusion casting, and halted aging process. He now lives in solitude serving as a scientific advisor for SHIELD, kept company only by trophies and mementos of past adventures.
But that doesn't mean his story is done. He still has an important role to play with this new team of Avengers. For he has first hand knowledge of the Eternals. He knows of Thanos.
And what Thanos has planned for the Dreaming Celestial.