Supergirl” gave comic book fans an unexpected treat in December when the show revealed that prickly DEO boss Hank Henshaw (David Harewood) was actually DC Comics favorite (and Justice League founding member) J’onn J’onzz, the Martian Manhunter. Since then, we’ve gradually learned more about the secretive alien revealed to be the last surviving member of his kind, but the January 25 episode, “Strange Visitor from Another Planet,” will turn the focus firmly on J’onn, as he becomes a target for a very different breed of extraterrestrial — the vicious White Martians, who are determined to kill J’onn the way they eradicated much of the rest of his species.

Below, British-born thesp Harewood discusses the parallels between “Supergirl’s” anti-alien debate and America’s current political climate, discovering the real Hank Henshaw, and what he most relates to about J’onn’s journey.

Once you discovered the truth about J’onn’s identity, was it easy to separate him from Hank and see yourself fully as J’onn playing a role?

I always knew that he was playing somebody that was reasonably unpleasant, and it was difficult because I knew further down the line that that wasn’t who he was really. But it was kind of tough because I was getting slaughtered on Twitter and people were saying how unpleasant I was and how horrible I was and how boring I was and how bland I was, and then the morning after I was revealed, people were like “oh my god, this is the greatest thing since sliced bread and he’s a wonderful character.” So it’s been wonderful, I’ve had a taste of both things. I always knew, reading the bad stuff, “they’re gonna be saying something different in a couple of weeks.”

I would always go to work as “Hank,” but reading about J’onn J’onzz gave me everything I needed to play Hank Henshaw, because in the pilot I was very uncomfortable. I didn’t know who Hank Henshaw was in the pilot; I could even see by the pictures that were taken of me at the time, I didn’t know who I was – they hadn’t given me a backstory. Even though Hank goes on to be Cyborg Superman, I couldn’t find any characteristics of Hank Henshaw – it was a real struggle for me. So as soon as I knew he wasn’t Hank Henshaw, he was J’onn J’onzz, all the mythology supported everything I was doing and I was much more secure about it.

This week’s episode, “Strange Visitor from Another Planet,” introduces the White Martians — for the DC Comics uninitiated, what differentiates them from J’onn’s race of Green Martians?

The Green Martians are much more communal, more peace-loving, they’re all about living together, learning and growing. The White Martians exist purely to kill Green Martians. They are the same species but a separate race – they only have one purpose and that’s to kill. They’re not interested in peace, they’re not interested in dialogue, they’re not interested in living together – they just want to kill Green Martians. They’re a very violent, very aggressive species, and once they find out that there is one still alive, they just want to kill him.

We’ve already seen stirrings of anti-alien sentiment from Maxwell Lord (Peter Facinelli) on the show, and tonight’s episode introduces Senator Miranda Crane, (Tawny Cypress) who has a virulent anti-alien agenda. Will we see this growing suspicion about aliens continue to build throughout the rest of the season and become more of a concern to Kara (Melissa Benoist) and J’onn?

I think we will. It’s really interesting, you’ve got, politically, this very interesting strain of Republican politics talking about aliens and talking about walls and talking about “them” and “us” – and a lot of that plays into what we’re doing on “Supergirl.” People are afraid when strangers land on their door… people are afraid when they’re aware somebody is different from what they are — we play with that, not only with J’onn. That’s one of the reasons why he wants to stay as Hank; he knows full well, unlike Kara, he can’t just openly come out and live as he normally is because [firstly] he’ll be arrested for treason — he’s leading a government organization so first off he’s broken a law there — and secondly he knows what the reaction will be if people find out who he really is. People get angry when they realize their husband or wife’s having an affair, but to know that somebody has betrayed you because they’re not actually who they say they are… he’s aware of all those things. So he’s actually a little afraid of it, because the more he’s exposed as J’onn J’onzz, the less people are gonna be willing to listen to him.

We’ve seen the damage J’onn inadvertently caused to one of Max Lord’s employees when J’onn tried to erase his memories — will he continue to struggle with using his abilities?

I’m playing it as though he hasn’t used those powers in many, many years. Since he’s been Hank Henshaw, he’s probably not used any of his powers, so in my mind, he’s just getting used to them again, just as Kara had to get used to the intensity of her heat vision and freeze breath – just as she had to learn how to control those powers, I think J’onn is in the same position. He’s having to relearn how to be the Martian Manhunter, and a lot of those powers he hasn’t used before. Over the course of the season, he’ll get better at it.

We’ve seen J’onn express some envy that he can’t be himself the way Kara can because he doesn’t look like a pretty blonde, and we’ve seen her ongoing struggles to reconcile both halves of her identity. How does she help him embrace his alien side going forward?

Throughout the season we see him becoming more and more comfortable with the J’onn J’onzz part of his character, and we also see Kara teach him a little bit more. Particularly at the end of Monday’s episode, she says something which lands on him very strongly which is that yes, he is the last son of Mars, but that doesn’t mean he has the right to besmirch the name of those Green Martians. He has to be honorable, he has to make them proud as opposed to wreaking havoc and revenge — perhaps he should take the high road and not stoop to the level of what the White Martians may or may not have done.

I first became aware of J’onn through the “Justice League” cartoons, and he quickly became one of my favorite characters because he has such a pure, good heart. Despite the immense loss he’s suffered, he still has such care for humanity and a desire to see the best in them, which I always appreciated. I was curious what aspects of his character you value most or gravitate towards in playing him.

I’m exactly the same — I was really struck by that; I love the fact that he has the internal dialogue running through his comic book where he’s just questioning mankind, questioning his own existence and the existence of pain and death and life. He really has taken humanity into his heart and questions why they make the decisions they do, why they do the things that they do. One of the things that struck me was that he has this immense melancholy, this sense of loneliness, this sense of isolation. I have two kids and they’re in London and I’m exactly the same, I wander around having this internal dialogue thinking about America, talking about politics here in America, talking about the beliefs here in America, so I’ve really associated with it. That’s one of the things I’ve taken to heart, this sense of isolation, and being okay with the isolation. Yes, I’m lonely, but it’s okay to be lonely – I listen to music or I read books or I go for walks, all the time I’m thinking about that sense of isolation that J’onn has, so there’s always a little part of him that’s not there, he’s somewhere in his own head and I draw on that to play the character. It’s just been a real pleasure to find a character that I didn’t know about with such an incredible mythology and backstory. I spent eight hours reading J’onn J’onzz comic books and I’m just amazed about his abilities and I’m amazed that he’s such a wonderful rich soul. He’s a lovely, gorgeous character.

We’ll also get a chance to see the real Hank Henshaw later this season via flashbacks — what’s he like?

It’s been a lot of fun playing the real Hank. The real Hank Henshaw is something of a sadist. We see that in 117, we saw flashbacks a little bit in 105, but you see full well how he became Hank Henshaw, and you get more of a glimpse of the real Hank Henshaw. He’d be a lot of fun at the Christmas party but I’m not sure you’d want to sit next to him on the train to work. He’s a bit of a maniac. [Laughs.]

“Supergirl” airs Mondays at 8 p.m. on CBS.