• Michael Fassbender thought he'd blown a "surreal" audition with Quentin Tarantino.
• The star told Business Insider what it was like working with the director on "Inglourious Basterds."
• He said he originally wanted to play Christoph Waltz's Nazi villain, Hans Landa.

Michael Fassbender was convinced that he'd blown a "surreal" audition with Quentin Tarantino when he went out for a role in "Inglourious Basterds."

Fassbender rose to fame in the 2000s, with roles in films like "300," "Hunger," and "Fish Tank." However, playing British film critic-turned-soldier Lt. Archie Hicox in Tarantino's 2009 film "Inglourious Basterds," about a group of soldiers who set out to execute Hitler during WWII, was what really pushed him into the spotlight.

When speaking to Business Insider, Fassbender recalled how he originally wanted to play Nazi officer Hans Landa (Christoph Waltz), the terrifying villain who takes great pride in hunting Jewish families throughout Europe.

"Originally, I wanted Landa! I had prepped about 27 hours of Landa," Fassbender said. "I was shooting 'Fish Tank' at the time, and my agent said 'They'd like you to look at Hicox as well.' And I was like, 'I'm not going to have time to do both.'"

The actor flew himself over to Berlin to audition for Tarantino.

"I came into the room and Tarantino said, 'Okay, let's take a look at Hicox.' I said, 'Do you think I could read for Landa?' And he was like, 'I cast Landa on Tuesday.' I was like, 'Okay, let's read Hicox…," he recalled.

Fassbender said that he auditioned with Tarantino reading the other lines, and the "surreal" experience left him feeling like he'd blown the opportunity.

"I did a cold reading of it basically, and he read the other parts, which was super surreal and kind of intimidating. But I just went for it and I was pretty sure I blew it," Fassbender said. "I called my parents straight away after I came out and I was like, 'I blew it. I messed it up.'"

Despite Fassbender's perceived failure, he won the role and cemented himself in one of Tarantino's most memorable scenes: the Mexican standoff between the Basterds, and a bar full of Nazi soldiers.

Fassbender said that his costar August Diehl, who played the sinister Gestapo major Dieter Hellstrom, was "phenomenal," which made him determined to deliver a great performance.

He said: "From day one in rehearsals, he was off-book and I was like, 'Okay, I better get my shit together. This guy's great.'"

Over 15 years later, Fassbender has become an A-list actor in his own right, starring in huge franchise movies like "X-Men" and "Alien," but he still looks for complex roles.

His most recent project, Showtime's "The Agency," sees him play a deep-cover CIA agent named "Martian" who returns to the London office after six years in the field. The show, which premiered in November, has already been renewed for a second season.

The actor was keen to explore the layers underneath Martian's cold, stoic exterior in the series.

"I think he's kind of crawling in his skin, but he can't show it. So everything is always hidden. The idea of when he's telling the truth and when he's lying, I'm not even sure he's aware of that, and the idea that he's also unhinged," he said.

Fassbender added that for him, a complex character is a welcome challenge.

"I try to see something new, something that scares me a little bit. I always feel like, 'God, I can't do this' and just to keep the challenge element alive, I tend toward characters that are complicated," he said.

"The Agency" is streaming on Paramount+.