LOS ANGELES — A lot of factors go into Steve Carell’s process of selecting scripts. In the case of “Vice,” the production played into his long fascination with looking at the past, which includes being a history major in college.

The film from director/writer Adam McKay opens the history books as it looks at the rise of politician Dick Cheney (Christian Bale), who manipulated and exploited to turn his vice presidential role to George W. Bush (Sam Rockwell) from a mostly ceremonial job into becoming a major player in policy and decision making. Carell plays former Secretary of Defense Donald Rumsfeld, who was both a mentor and friend to Chaney.

“I connected more with (the script) in the sense that it’s a historical document,” Carell says. “One of the things I learned as a history major is that you are certainly at the mercy of whoever is writing the history and it can change your perspectives on any historical accuracies.

“As I go further into my years as a history major, that’s mostly what we were learning — to try to disseminate what is truth and what is fiction.”

His interest in questioning what he reads has played into his work as an actor. Whether it’s a light comedy such as “Bewitched” or a script based on the life of a real person such as “Vice” or “Foxcatcher,” Carell has always felt compelled to do research to have the best understanding of the role.

He calls doing the research an “effort to make the most accurate guess possible.” In the case of playing Rumsfeld, Carell read Rumsfeld’s autobiography, keeping in mind that the book was written from a specific point of view. Carell took researched further by reading books and articles written about Rumsfeld, watching a documentary that featured the politician and looking at news footage.

All that helped appease Carell’s cravings for historical matter, plus it gave him a chance to see how Rumsfeld moved and hear how he talked. After he had the material, Carell then had to weigh it against his own views.

Going into his research, Carell knew historically politicians have a public and a private persona, which tend to be very different. His research of the public material about Rumsfeld showed him to be “like a friendly uncle.” But, except for a few accounts that described Rumsfeld as a formidable advisory behind closed doors, Carell ended up mainly hypothesizing what Rumsfeld was like when he wasn’t dealing with the public.

“You don’t want to turn a character into a villain. You have to look for the humanity in everybody you play,” Carell says. “I certainly tried to do that with Donald Rumsfeld. I do think he was an aggressive person. He was a very straightforward person who did not mince words. He was extremely confident in his own point of view.”

One thing that’s similar in every role Carell tackles is he has to feel a connection to the story and character. What creates the connection could be one of a litany of factors, from who is directing to what is happening in his life. Along with his passion for history, Carell jumped at the chance to be in “Vice” because he would be working with Adam McKay.

“Vice” is just one of three films for Carell at the end of 2018. Each shows a different side of his acting. Along with “Vice,” Carell stars in “Beautiful Boy,” playing a distraught father who deals with his son’s addiction. And with “Welcome to Marwen,” he takes on the role of a man who seeks solace in a special world after a brutal attack.

Carell has been acting for more than two decades, but it wasn’t until the last few years that he began to look at what it was that made him agree to so many different roles.

“I think sometimes it is not even that you think it is right for you as an actor but whether it is right for you emotionally at the time,” Carell says.

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As an example, Carell points to how he agreed to star in the emotionally charged “Last Flag Flying” in 2017 because he was offered the role just after his mother died. It felt right to him to play a Vietnam vet who reunites his buddies from the military to help him bury his son, a Marine killed in Iraq. There was sadness in his life that made the film the right choice for him in the moment.

He agreed to be part of “Beautiful Boy” because it’s a very timely story.

“I tend now to take things that kind of scare me a little bit,” Carell says. “I believe that it keeps you on your toes. The whole subject matter of ‘Beautiful Boy’ scared me because I have two teenagers. I fortunately haven’t had to go through something like that, but the theme is terrifying. In that way it felt like something that stirred me up inside.”