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.

Personality
""Here's the truth, a reporter got greedy for a scoop and went where she shouldn't have. Superman acted like some rogue combatant to rescue her, and people died. Don't invent a conspiracy theory to put back his halo. Or yours.""

- ― Calvin Swanwick to Lois Lane

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.

Powers

 * Martian physiology: As a Martian, Martian Manhunter is outwardly humanoid, but there are clear distinctions between him and humans, such as green skin, ridged patterns on his body, and bright red eyes in his true form. Inwardly, there are even more differences, with Martian Manhunter possessing many superhuman abilities.
 * Shapeshifting: Martian Manhunter is able to change his appearance or form at will to resemble any other being of his choice, such as his Swanwick persona, or Martha Kent. He was able to masquerade as the human Swanwick for many years without being exposed. When he chooses, Martian Manhunter's red eyes come through in his disguises. He can also change his voice to suit the person he impersonates.
 * Flight: Martian Manhunter, much like a Kryptonian, is capable of high-speed flight.
 * Telepathy: Martian Manhunter is a telepath, capable of looking into the minds of those around him. He uses this ability to discern that Bruce Wayne is the leader of the Justice League, so he can approach him directly to offer his services in protection of the Earth.

Abilities

 * Expert actor: Martian Manhunter is a excellent actor, able to pose as the human Swanwick for years without suspicion, and even fooled Lois into thinking that he was Martha Kent.
 * Expert tactician: Martian Manhunter is a highly intelligent individual, an excellent tactician and leader.
 * Expert leader: As a Lieutenant General in the United States Army, Swanwick is able to efficiently lead and order other soldiers out in the field.
 * Indomitable will: Martian Manhunter was unafraid of the godlike Superman (eventually befriending him), and was not intimidated by Faora.

General

 * In Man of Steel, Swanwick is the first non-Kryptonian to mention Krypton by name, despite never having heard the planet's name on screen. Whether this is a nod to Martian Manhunter's mind probing capabilities, coincidence, or alien knowledge isn't clear.
 * Since the gap between Man of Steel and Batman v Superman: Dawn of Justice is shorter than seven years, it's not traditionally possible for General Calvin Swanwick to serve as United States Secretary of Defense due to the National Security Act of 1947 which prohibits anyone who has been active in the military within the past seven years from taking the position. This is to ensure civilian control of the military. Either the rules of the position are different in the DCEU, or a special waiver of some kind was granted.
 * Coincidentally, in real life, Lloyd Austin, the 28th U.S. Secretary of Defense bears a similarity to the Calvin Swanwick character. Both are African-American who served as Secretary of Defense and former High-Ranking U.S. Army officers, Swanwick is a retired Army three-star Lieutenant General and Austin is a retired Army four-star General. Both Swanwick and Austin also once held command position within the United States Unified Combatant Command, a United States joint military command that conducts broad and continuing missions worldwide. Swanwick as Deputy Commander of the United States Northern Command (USNORTHCOM) with Area of Responsibility within the United States and North America and Austin as Commander of the United States Central Command (USCENTCOM) with Area of Responsibility within the Middle-East and Central Asia. Both Swanwick and Austin haven't retired from active-duty for minimum period of Seven years by the time they both served as Secretary of Defense which required by United States Law of National Security Act of 1947. While Austin did received waiver from both Congress and Senate to assume the duty of Secretary of Defense before retiring from active-duty for minimum period of seven years in the real-life, it is unclear whether Swanwick also did receive the same waiver from both Congress and Senate to assume the duty of Secretary of Defense before retiring from active-duty for minimum period of seven years, since the rules of the position might have been different in DCEU. But if the DCEU and real-life rules are indeed the same, so therefore Swanwick might have also received waiver from both Congress and Senate to assume the duty of Secretary of Defense before retiring from active-duty for minimum period of seven years, similar with Lloyd Austin, the incumbent Secretary of Defense in the real-life.
 * The Martian Manhunter's most common human identity is that of detective John Jones (an obvious American adaptation of his Martian name), who is typically depicted as African American in recent years.
 * Disguising himself as an African American United States military official, serving as a liaison between a Kryptonian and the government, and his identity being someone other than John Jones are all similar to his secret identity as Hank Henshaw, director of the DEO in the Supergirl TV series.
 * His suit is seemingly inspired by the Superman skinsuit with similar muscle definition, similar markings near his waist, and similar boots and a cape.