Martian Manhunter (David Harewood)

J'onn J'onzz is the sole survivor of Mars. After being discovered on Earth, J’onn was tracked down in a remote location in Peru by the D.E.O. However, Jeremiah Danvers saved J’onn's life by giving his own to stop Hank Henshaw, with J’onn promising to watch over Alex Danvers thereafter. Disguising himself as Hank Henshaw, J’onn took over as the head of the D.E.O.

History
The D.E.O. subdued Supergirl as she was mid-flight on her way to stop a fire. After she woke up at their base J'onn, as Hank Henshaw, introduced himself as the organization's director. After being released from kryptonite cuffs, J'onn explained to Kara how her ship brought Fort Rozz to Earth when it escaped the Phantom Zone, and released thousands of the galaxy's worst criminals. Afterwards, Hank rejected her offer to help capture them, telling her that if she wanted to help, she could go back to getting someone's coffee. Henshaw later sarcastically remarked on how Kara did in fact help, after she was defeated by Vartox and her wound opened up a possible way to ID his weapon, potentially giving the D.E.O. a way to defeat him. Later, Hank was convinced by Kara to let her intercept Vartox, after the satellites picked him up heading towards National City, with him telling Kara, "Make sure you win." He was later questioned by Alex Danvers whether she was solely recruited based on Kara, with Hank telling her that, that was in fact the reason she was recruited, though she was the reason she got to stay within the organization.

A week later, J'onn along with the rest of the D.E.O. tested the limits of Kara's abilities, as he needed to know that she was in full control of her powers. The next day, J'onn questioned what Kara was doing at Plastino Chemicals during a D.E.O. investigation, though after the situation was explained to him by Alex, he told Kara not to touch anything. At the D.E.O. base, Kara told J'onn and Alex that the alien they were looking for was a Hellgrammite. J'onn was offered by Kara that the D.E.O. could track the Hellgrammite down, and Kara could defeat him, though J'onn came to the declined saying she could do so if she could prove to them that she could handle herself without being killed. The following day, J'onn along with Alex and Agent Hartmann came to the conclusion that the Hellgrammite was eating the DDT he had been stealing, as the government had been destroying remaining stockpiles, and his food source was shrinking. Later, the DEO set a trap for the Hellgrammite with a truck driving with tanks of DDT in it's back, and Alex and J'onn along with several other DEO agents followed behind it in another vehicle. Soon after Alex was abducted by the Hellgrammite, forcing J'onn to call Kara back the D.E.O. base. He was later berated by her for putting her through tests instead of trusting her, as the situation could have been prevented if she had been there. J'onn however reassured Kara that they had every satellite and a tactical drone searching for Alex. J'onn was later alerted to Alex's position after Kara discovered it through the use of her super hearing. Though he warned her to wait after she told him he that she was going to get Alex, he was ignored. J'onn later rescued both Alex and Kara from Astra, ordering the Kryptonian to halt. Though Astra grabbed J'onn by the neck, taunting that he had no weapon that could hurt her, he plunged a kryptonite knife into her arm, prompting her to fly off. J'onn was later thanked by Alex for helping her setup the room in the D.E.O. base that Kara could talk with the AI that was found in her pod.