Martian Manhunter

J'onn J'onzz, known by some as the Martian Manhunter, is an alien from Mars that eventually traveled to Earth and posed as a Lieutenant General named Calvin Swanwick in the United States Army, and later as Secretary of Defense. He was present at the time of the Black Zero Event in 2013, holding the position of head of United States Northern Command, and being tasked with preventing any possible threats towards the United States and her interests.

Hence, he formed an alliance with the alien hero Superman in order to defeat the extreme threat posed by General Dru-Zod and the Sword of Rao.

At some point during the two years after the Kryptonian invasion, Swanwick was promoted to United States Secretary of Defense, and he became a reluctant ally to Lois Lane's investigation into the Nairomi incident. He later attempted to aid Superman again, this time against the monster Doomsday, though his efforts were ultimately unsuccessful.

After Steppenwolf's invasion and defeat, the Martian Manhunter revealed himself to Bruce Wayne, warning him of an impending retaliation from Darkseid and his forces.

Coming to Earth
At some point, J'onn J'onzz traveled from Mars to Earth, and took up a human appearance and identity, naming himself "Calvin Swanwick". He acquired the credentials that identified him as a five-star general of the United States Army. As part of his duties, he dealt with terrorists and rogue nations. Martian Manhunter might have met Thomas and Martha Wayne at some point, as he later assures their son Bruce that they would have been proud of his efforts.

General Zod’s message
General Swanwick was alerted to the mission control room at Peterson Air Force Base when a huge UFO settled into orbit near Earth. Shortly thereafter, a menacing message was sent all across the Earth from the extraterrestrial General Zod, who demanded that a fellow alien from his planet, a man named Kal-El(who had tried to blend in with Earth's population for decades), be handed into his custody, and that if the latter wasn't turned in to Zod within twenty-four hours, the entire planet would suffer severe consequences of apocalyptic proportions. By the time the message ended, General Swanwick was already on the phone with someone at the White House. He informed that person that the Joint Emergency Evacuation plan would be activated, while advising against the use of Air Force One because the skies probably weren't safe at the moment.

Kal-El’s surrender
Kal-El himself arrived at a military base shortly afterwards, surrendering if Lois Lane was to be freed. Kal-El and Lois sat in an interrogation room where the General questioned Kal-El on his motives, before handing him over to General Zod's second-in-command, Sub-commander Faora-Ul, who requested that Lois come, too.

When two bogies descended from the General Zod's starship into Earth's atmosphere, Swanwick order a strike to take them out, led by Colonel Hardy.

Defeating the invaders
After the Battle of Smallville, Kal-El (now nicknamed "Superman") and Lois came, along with Kal-El's Spaceship, telling the General how to send Zod and his followers back to the Phantom Zone, this time permanently. The plan was to collide the Phantom Drive of Superman's infant starcraft with the Black Zero's, in an attempt to create an unstable Phantom energy singularity, which would suck all of Zod's forces back into the Zone. Before they could do so, however, Superman would have to personally destroy Zod's World Engine and end Earth's terraformation. Swanwick agreed to the plan and ordered the attack, after which Superman promptly took flight to the Indian Ocean.

Ultimately, while the plan was successfully executed (with only General Zod remaining on Earth), it came at the cost of Colonel Hardy and Dr. Hamilton's lives, with only Lois escaping the singularity's pull, due to Superman's timely intervention. Nonetheless, Earth and all of humanity had been saved from the alien invasion.

Official alliance with Superman
Shortly after the end of the Kryptonian invasion, General Swanwick had drones try to track down Superman's whereabouts, determined to find his address. Superman, however, wasn't pleased, and proceeded to slam one of the drones into the ground, right in front of Swanwick's car, much to the latter's dismay. Superman assured the general that, having grown up in Kansas, he was technically an American himself, so he would never act against the United States' interests. However, while Superman would always remain an ally to both America and all of Earth, he requested that it be done on his own terms, and that he trusted Swanwick's ability to convince Washington D.C. of that. With that said, Superman took flight again at supersonic speeds, leaving Captain Farris smiling, self-admittedly in awe of the handsome alien.

Promotion
At some point during the two years after the Black Zero Event, Swanwick became promoted from general to United States Secretary of Defense.

Helping Lois Lane
After the incident in Nairomi, Lois Lane approaches Swanwick (meeting him in the men's bathroom), telling him that the bullet that she had obtained in the incident is not made by any known manufacturer. Swanwick was upset over the incident in Nairomi, stating that Lois went there because she was greedy and Superman was responsible for the deaths of the people there, after he went in to rescue her, he eventually gives in to Lois's persistent requests, and identifies the bullet's maker. When he meets her next, Swanwick reveals to Lois that it is a special prototype ammunition made by LexCorp Industries.

Battle against Doomsday
Later, after Lex Luthor successfully creates the mighty Kryptonian monster Doomsday, Swanwick, as the Secretary of Defense, communicates with the US President about how to respond to the new threat. The president, in desperation, orders the alien monster to be shot down with a nuclear missile, and while Swanwick protests (not wanting his ally Superman to be killed as well), he is overruled and the missile is fired, colliding with the fighting alien juggernauts right above Earth's atmosphere, and temporarily incapacitating them. However, right after the wounded Doomsday falls all the way back to Earth, he heels and rises up to his feel almost at once, and unleashes a tremendous electrical shock-wave from his body, more powerful than the ones before it. Swanwick gravely notes that Doomsday is apparently unkillable, as the attack has only made it stronger.

The Kryptonian monster is, however, ultimately defeated by the combined efforts of Superman, Wonder Woman, and Batman, though Superman himself seemingly dies in the process.

Superman’s funeral
At Superman's grandiose military funeral, Swanwick, along with Carrie Farris, is seen among the many that mourn his death. Afterwards, Swanwick is presented the folded American flag that was over Superman's (empty) casket during his military funeral.

Visiting Lois
Many months after the death of Superman, Swanwick disguised himself as Martha Kent and went to visit Lois Lane in her apartment. There, he revealed that the Kent farm had been foreclosed because Martha had fallen behind on payments. The two briefly discussed Superman's legacy only as a symbol and lamented how nobody really knew Clark the way her and Martha did. The Manhunter then encouraged Lois to move past her grief and "come back to the living".

After talking, he leaves the apartment and shape-shifts to his true Martian form, and then to Swanwick, whispering that the world needed Lois as much as Superman, before leaving.

Warning Bruce
One morning, sometime after the Justice League defeated Steppenwolf, he flew over to Bruce Wayne's house and although he was impressed by their victory, he warned Bruce that the fight was not over yet, and Darkseid would eventually make his way to Earth. Bruce inquired as to who he was, and he notes that he was known by many names, one of which was the Martian Manhunter. He also mentioned was ready to step out and start fighting, now that there were more heroes in the world. Following their little talk, he flew off into the distance.

Personality
His Swanwick persona, while somewhat gruff, is, as an illustrious member of the US Armed Forces, and is quite patriotically dedicated to his job and country even if that sometimes makes him unwilling to compromise said job, notably with his initial unwillingness to speak of Lex Luthor's innovative bullets on record. Swanwick does, however, place national and global security above all else, being more than willing to join forces with Superman (an alien whom he initially mistrusted) and help the latter carry out an elaborate plan, as long as that meant defeating General Zod's invasion.

After Zod's defeat, Swanwick gradually gained a great deal of respect and admiration for Superman, speaking to the US government on the latter's behalf, disbelieving Kahina Ziri's slandering rumors about Nairomi, and covertly helping Lois Lane expose Lex Luthor's involvement. Swanwick displayed his great loyalty to Superman again during the battle with Doomsday, imploring the US president not to nuke the alien hero. Superman's death devastates Swanwick, who shows his immense posthumous respect during the former's military funeral.

In his true identity as Martian Manhunter, he is less gruff, but still serious and pensive.