Step Brothers was made by and for Will Ferrell and John C. Reilly. The true origin of this hilarious film came from Will and John's experience making Adam McKay's Talladega Nights: The Ballad Of Ricky Bobby. The entire film was designed around what these two legendary actors wanted to do. They were front and center as the film's title suggests. But that doesn't mean that attention wasn't spent on finding the right people for the supporting cast.
Will Ferrell is well aware of the importance of a strong supporting cast in a comedy. After all, he was one of the best parts of Wedding Crashers despite having only a couple of scenes. But hiring the right actors for Step Brothers was a little trickier. This is why...
The Supporting Cast Had to Be Able To Deal With Improv
According to an interview by The Ringer, writer/director Adam McKay and co-stars and co-writers Will Ferrell and John. C. Rielly needed to make sure they found actors who could improvise. Or, at the very least, these actors needed to be able to play off of Will and John who were and are notorious improvisers. In fact, much of the dialogue in the best scenes in Step Brothers was improvised.
"I would warn every actor: 'Before you take this role, I’m gonna have you improvise. I’m gonna throw ideas at you. We’re gonna mess around.'" Adam McKay told The Ringer.
Regardless of trying to find actors who could improvise, Will, John, and Adam kept coming back to Academy Award-winner Mary Steenburgen for the role of the mother/step-mother. While she wasn't famous for improv, she had appeared on Curb Your Enthusiasm where she had to improvise with Larry David and her real-life husband Ted Danson. Additionally, she had filmed a movie with Will before.
"Will and I did Elf together, and we had a great time," Mary Steenburgen, who played Nancy Huff, said. "He called me and said, 'Would you feel insulted if I asked you to play my actual mom?' I think I’m, like, [14] years older than him."
Around the same time, they found Richard Jenkins, who was on his way to becoming a massive star. While Richard wasn't obviously funny, he was 'earnestly' funny which perfect for the role of Dale, the father/step-father.
Casting Adam Scott And Kathryn Hahn
The other characters Will, John, and Adam were considered with Will Ferrell's Brennan's jerk of a brother (Derek) and his very full-on wife, Alice.
"Getting the role was a total fluke," Derek's Adam Scott, now famous for his work in Parks and Rec and Big Little Lies, said to The Ringer. "I hadn’t really done any comedy at that point. Step Brothers is 100 percent my foray into comedy."
"Adam was the one we didn’t know," Adam admitted. "But [Step Brothers producer] Judd [Apatow] had worked with him. And Paul Rudd and Jon Hamm [who also read for the role] were friends with him. And Paul Rudd just told me: 'Adam Scott’s one of the funniest guys I know.' And if Paul Rudd’s saying that, you know he’s good."
Still, nobody knew just how funny Adam Scott was until he showed up on set and starting improving with Will and John as well as with Kathryn Hahn's Alice.
"Kathryn Hahn had done a small part in Anchorman. We knew she was amazing," Adam said.
"Allison Jones is such a champion casting director," Kathryn Hahn said. "She had a very, very, very small room. It was [McKay], me, and John C. Reilly. And I had never met John. Boogie Nights! I was just obsessed. I remember I brought a bag. That was my little armor, I think. It was like my Dumbo feather. I didn’t think I could fly without it."
During the casting sessions, Adam McKay would get improvisers to read with each of the actors just to see how they could handle the skill. This was like a little trail for when they eventually got a call-back and worked off of Will and/or John.
While many actors impressed during the improv at the auditions, it was WandaVision's Kathryn Hahn who really blew everybody away. Therefore, she was brought in to improvise alongside John. This is when she hilariously crossed a few lines, which actually impressed the casting director and Adam McKay.
"It got really dark and really gross, really fast. There were a couple of takes where we got really detailed on how to kill Adam Scott’s character. It was very To Die For," Kathryn admitted. "There’s this feeling where all of a sudden you bust through what’s expected and you just take off on this path with them. We went on forever on the weirdest tangents. I definitely walked out of there like, 'I’m never gonna get it, but that was the most fun. I can’t believe I got to improvise with John C. Reilly.'"
Of course, Kathryn ended up getting the role and got to work with Will, Adam, John, Mary, Richard, as well as Andrea Savage, Ken Jeong, and even Seth Rogen.
Now, that's an all-star cast.