When it comes to Simmons and Fitz's budding romance on "Agents of S.H.I.E.L.D.," Will Daniels remains the big elephant in the room. While trapped on the planet Maveth, Simmons fell in love with stranded astronaut, Will Daniels. Simmons managed to return to Earth and despite her escalating feelings for Fitz, vowed to rescue Will and save him from the evil entity dwelling there. However, Will's identity has currently come under fire. Could he be an Inhuman? Or, worse, a Hydra agent?

RELATED: Dalton Teases A "Crazy" "Agents of SHIELD" Midseason Finale

"Nikita" alum Dillon Casey, who plays Will, grew up on a steady diet of superheroes and comic books, making his "Agents of S.H.I.E.L.D." guest-starring role a plum assignment. Ahead of tonight's winter finale, Casey spoke with CBR about the secrecy surrounding his character, coming between Simmons and Fitz, and surviving the extreme temperatures while shooting on location. He also opened up on about his upcoming MMA fighting flick "Only I," and his desire to play a familiar X-Man.

CBR News: How secretive was the audition process about who you were playing and where your character fit into that initial episode, "4,722 Hours?"

Dillon Casey: Honestly, I didn't know anything about it. When I initially got the audition sheet -- sides, as they call them -- I read it and it struck me that Will was lost in some cabin in the woods. It read like a scene out of "Evil Dead." That's how I interpreted it. I didn't know they were lost on some planet, and I didn't know what was chasing them. I don't even think they gave me the real name of the characters doing the scene. I knew nothing about it.

I got the script the day before shooting. I didn't know anything about the character before we got started. I knew that it was a big character. I knew that it was an important episode, but that's pretty well all I knew.

Will isn't an established character in the comics. How happy were you with his arc?

It was such an amazing opportunity to get to do a character like that. The show kind of took a break to focus on Elizabeth's character [Simmons]. Getting to play Will and have a whole episode focus on their relationship, I just felt like it was an incredible opportunity.

And what a cool character to play. The guy goes from literally being a complete madman to blossoming into a real human being by the end. It's an actor's dream. I got to do some action sequences in there, too. The best scenes you get to do as an actor is when you're sitting there talking with another actor, going moment to moment. I got to do a lot of that. It was a lot of fun.

"S.H.I.E.L.D." fans have been rooting for Fitz and Simmons to become an item. Were you worried about any backlash against Will?

Not at all. The best thing you can hope for is for people to have an opinion. Backlash is a good thing. The worst thing you can get is indifference. I wasn't aware of the whole shipping thing going on. I'm used to the shipping from "Nikita." I knew that was going to happen when I found out the whole back story of Fitz/Simmons. I kind of got a feeling, but that's a good thing. I was looking forward to the backlash.

Where did you shoot "4,722 Hours," and what were some of the challenges of bringing the planet Maveth to the screen?

The whole inside of Will's cave is all a soundstage. Everything else you see was out in the desert. We went to Simi Valley in this work quarry, which is where the majority of it was shot. The rest was filmed in Northridge, near the Mojave Desert. The biggest challenge was heat. As an actor, I don't have to be out in the heat all day; I just have to be in the heat between "action" and "cut." They give us a fan and a bottle of water. The challenge is for the crew. Those guys are working their asses off in this 100 degree weather. I couldn't believe they were able to do it. I'm out there whining after doing 20 minutes in the heat, while these guys are doing manual labor. The biggest challenge was definitely that.

The one point I got a little claustrophobic was when I had to put on the Apollo spacesuit. That was a real spacesuit, meaning it went from 100-degree heat to 180 degrees inside this thing. They put cooling packs on me, but it barely worked. For about an hour and a half, I was in this spacesuit, in the middle of the desert, just dying. At the same time, it was so cool to be able to wear one of those things and get to do that for a job. There were challenges, but they were fun.

At the end of the episode, Simmons returned home while Will was left stranded on the planet. How much did the producers reveal about Will's fate and his inevitable return at that point?

I had no idea. I don't know what I'm allowed to say about his return. He might return, and he might not. It was on an episode-by-episode basis. I finished, and I just waited. I had no idea what was in store for the character. I had no idea what his fate was going to be. I probably only know a little more than the audience. They don't tell me much.

Plenty of theories are floating around the Internet: Will is the Inhuman. He's Hydra. There's a clandestine reason he was chosen for this mission. What's been your favorite speculation?

As a kid, I was introduced to the movie "Forbidden Planet," where the alien is the Id of the crew. I like that theory, that Will is actually the Id, just because it's nostalgic and a cool part of science fiction. I can't give anything away, so I don't want to hint at what the closest theory is. It's surprising what the audience can come up with. They are a smart audience.

"Closure" ended with Coulson, Fitz and Ward on Maveth. How much interaction does Will have with them?

I don't know how much I can tease you about that. Most of his interaction, interestingly enough, comes with Fitz. That's going to be really fun for the audience to see, especially for all those Fitz/Simmons shippers out there.

As Sean on "Nikita," you demonstrated some killer combat moves. Did you get your adrenaline fix in this episode?

There's one especially cool moment near the end that is going to turn out pretty epic. It was exciting, so I got an adrenaline fix there.

Your movie "Only I" is waiting for a release date. Who do you play and what attracted you to the project?

"Only I" is a story about an underground MMA fighter who is throwing everything he's got into being a fighter and giving it a serious shot. I play his rival, sort of the Apollo Creed character to his Rocky.

What attracted me to it is, I was doing "Nikita" at the time. I was really into mixed martial arts. It's a bit of a hobby of mine. I was interested in doing a movie like that. Basically, everything I do in that movie is a fight scene. I thought it would be interesting to get out there and have a really physical part.

In the trailer, it appears you whale on co-star Brendan Fehr.

Yeah, and Brendan whales on me, too. It was grueling. That was one of the hardest things I've ever done. We'd have these shots that would go all night. I'd be shooting "Nikita" during the week, and then I'd have a day off and go film "Only I." It would be a whole night of just fighting. It was exhausting. We'd do one take, where we'd get to the set and were able to do everything we had been rehearsing, and had 12 hours of that to do. I'm looking forward to seeing the movie and how it turned out.

Growing up, what was your connection to superheroes and comic books?

I was hugely into Marvel. I went through a really intense Marvel phase where I had every Marvel card. They used to have these cards where they had the superheroes, and on the back it had their measures of strength, agility, stamina and intelligence. You could basically get every superhero Marvel ever created. I had the full set with the holograms. It's always been a part of my life. Of course, I grew up watching a ton of movies and I used to love the superhero films. There wasn't as many when I was younger, but I always loved the hero character. I love Indiana Jones and "Star Wars," so I've always been a huge fan of those larger-than-life characters in that larger-than-life world. I was heavily into comics. I got into Dark Horse, DC, Marvel and the whole thing.

I always loved Wolverine and still do. I remember when the cartoon was on. I like those bad asses with a heart of gold. They are the guys that don't want to be heroes, but they have to be.

After getting a taste of the Marvel Cinematic Universe, are you hungry for more? In what capacity would you enjoy being further involved in this sandbox?

In any way possible. It's a great world to be a part of and I'm lucky to have the opportunity. If they wanted me back, I'd welcome it with open arms. I'd love to be a superhero. Who wouldn't want to be a superhero? Maybe Iron Fist or Black Knight. I think I would make a great Wolverine, but they cast him to some no-name! [Laughs]