Supergirl, Season 1

Hank:
I am not Hank Henshaw. He died the same night as your father. The D.E.O. had been pursuing an alien for months. Not one of Fort Rozz prisoners, but an innocent one that was stranded on this planet. With the help of your father, the D.E.O. tracked the alien to a remote location in Peru. Henshaw led the squadron sent to terminate him.

Alex:
My father would never have been part of that mission.

Hank:
You're right. Jeremiah Danvers was a good man. He realized the alien we were hunting was no threat. He was a refugee, like your sister. Sole survivor of a lost world. Your father tried to stop the mission, but Henshaw was obsessed. He finally trapped the alien was hunting for so long. So, Jeremiah made the ultimate sacrifice. He gave his life to save that alien. Your father died a hero.

Alex:
That alien... Is that you? But how are you him?

Hank:
I am a shape shifter. When Hank Henshaw died, I assumed his identity to reform the D.E.O. But I also made your father a promise, that I would take care of his daughter. I recruited you so that I would honor that promise and protect you as if you were my own child.

Alex:
If you're not Hank Henshaw, who are you?

[Hank transforms into his Martian shape]

J'onn J'onzz:
I am the sole survivor of my planet. The Last Son of Mars. My name is J'onn J'onzz.