There were serious doubts when Jason Segel was cast as the tragic genius David Foster Wallace inThe End of the Tour.

Segel, 35, has made a career portraying affable, endearing personalities — from Gary, BFF to a muppet named Walter in The Muppets, to goofy Marshall in TV's How I Met Your Mother.

But in Tour (opens Friday in New York and Los Angeles), Segel steps up to the complex role of Infinite Jest author Wallace, who struggled with depression and killed himself in 2008 at age 46. The film depicts a five-day interview with Rolling Stone writerDavid Lipsky (Jesse Eisenberg).

"We sometimes buckle when someone we know takes on a more dramatic role," saysTour director James Ponsoldt. "Perhaps it shows the limits to our imagination."

The doubts have turned to accolades for a performance The Hollywood Reporter calls "heartbreaking" and even early awards talk for Segel.

Here's how Segel made the transformation.

Employing the hair and bandanna: Wallace's unorthodox look is striking right off and a significant discussion point in Tour. Segel couldn't grow his hair out while shooting the end of Mother, so he relied on hair extensions.

"You can take the bandanna, the long hair or those clothes, individually," says Segel. "But when they all came together, that's when I felt really comfortable to walk out as David Foster Wallace."

The filmmakers took pains not to fixate on a physical imitation of the author. "We basically tried to get as accurate as possible without making it feel like an impression or a sketch," says Segel.

Reading Wallace's work: The voluminous writings — especially Wallace's seminal 1,079-page Infinite Jest — were key to understanding the author. Segel, who wrote The Muppets and is working on The Lego Movie spinoff Billion Brick Race, started there.

"It's a massive undertaking as a reader. And that puts in perspective what a massive undertaking it was as a writer," says Segel.

Every week, he'd read 100 pages and discuss the work on Sunday with three friends in a book club. "It was one of the best experiences I have ever had," says Segel. "To have four people with different life experiences and having this (book) resonate speaks so much to the writing's universality."