Run, Barry, run. Ever since The Flash premiered in 2014, the Scarlet Speedster has taken on his share of powerful foes. However, none of them have hurt him as much as Eobard Thawne, the Reverse-Flash. He murdered Barry’s mother, got his father thrown in prison and manipulated his daughter, among many other evil deeds. Tonight, after nine thrilling seasons, everything comes full circle as Tom Cavanagh reprises his villainous role for the series finale. We recently had a chance to chat with Tom, who shared his experiences on filming the series finale, why Reverse-Flash is Barry’s greatest foe, and why the series will stand the test of time.

I'm going to start you off with a fun little icebreaker question. You've played a lot of characters on this show over the years. If they were all locked in a room, who would be the last one standing? And to make it fair, Thawne can't use any of his speed powers.

Oh, it would be the Reverse-Flash. Easy! What else you got? I like that you're starting off with a softball.

What was it like when you got the call to come back for the finale?

We went into it always knowing. This is like my third or fourth show with Greg Berlanti, and when he asked me to play the Reverse-Flash, the understanding was that we would try to go out the way we came in with Flash vs. Reverse-Flash. I knew it was coming, and it's always a great thing to put on that suit.

Has the plan for you coming back in the finale changed at any point in the last nine years? Will Thawne still play the same role in this episode that you and Greg talked about a decade ago? Or did it evolve?

He and Flash are always going to get after each other, you know? I think I've said before that you can't have a light without a dark to put it in. What is the light of Flash without the obstacles that he has to overcome and the darkness of the Reverse-Flash?

What is Thawne's state of mind when we catch up with him in the finale?

One of the nice things people who watch the show have gleaned from what I've tried to do on camera is that he, unlike some villains who are blinded by rage, enjoys the process. If he's going to destroy Central City and destroy the Flash, he is also going to have fun doing so. His state of mind is generally that he is somebody who tends to enjoy the intensity of the mayhem that he causes, and sometimes maybe all too much.

Do you have any fun behind the scenes stories from shooting this episode?

Yeah, there always is. There's always so much fun. When you start wrapping up a show, the episode takes on a different life in many ways. The thing you always knew was coming back, suddenly isn't coming back. I think it becomes emotional for people. A lot was happening off-camera with people trying to maximize their last moments with one another. Everybody's going to go their separate ways. And it was also goofing off with Teddy Sears, who plays Zoom, at 3:00 in the morning on a cool Vancouver night. The banter and repartee that I've had with the crew is always a constant, and the finale was no different.

What was it like in the moment after you shot your last scene, and you realized your time on the series was over?

I think that would be a question to ask Candice (Patton) or Grant (Gustin). For me, I sort of left after the sixth season. The nice thing about playing the darkness that you have to put the light into is that you always need Reverse-Flash. Batman needs the Joker, and Superman needs Lex Luthor. Playing the Reverse-Flash was a joy. Even as I left the show after six seasons, as he does, he just kept coming back. Having been gone, having decided to leave as a regular and then coming back to blow up Central City now and again, I think it was much different for me coming back to shoot the finale than it would have been for Grant, who had stayed for a full nine years. Those emotions may have been much different because they hadn't left. I think there was a lot of hugs and a lot of tears on the last day.

How do you feel the series has grown and changed over the last nine years?

That really is a question for the fan. For me, if you're in a long-running show then you're fortunate. It's a rarity. I've done this for three decades and I can count on the fingers on one hand any modicum of job security. With most television shows, you go in excited and hopeful, and oftentimes those dreams get dashed. You know, it's very difficult for a show to stick around. Some shows are extremely repetitive, other shows try to evolve, and then it's up to the fans to decide whether they like the course of evolution.

For our show, I was extremely grateful to be there at the beginning when you're uncertain about what the future will hold. On season one, if they were to cancel the show after seven episodes, it wouldn't have thrown me. Oftentimes, that’s how it seems to go. Very early on, Greg Berlanti was adamant about getting the story out there. It's extremely impressive to watch him break a story.

The Flash very early on just came out of the gate. I'll always be grateful that I've been a part of that first season of The Flash. Those are special moments when they happen, and it was a privilege to be part of it.

The Flash series finale airs tonight at 8 p.m. (7 p.m. CT) on The CW.