Playing Ruben in his new BBC series Half Man was "so far away from me and anything I'd done before", says Richard Gadd. "It terrified me."
The six-part drama, written by and starring Gadd, follows three decades in the lives of self-conscious Niall and volatile Ruben, who were once inseparable as teens.
Half Man explores the breakdown of their brotherhood and sees Niall struggle to accept his sexuality, while Ruben grapples with a trauma from his past.
Gadd explains he didn't initially see himself acting in the series after his "intense" experience with 2024 Emmy-winning show Baby Reindeer, in which he played comedian Donny Dunn.
The follow-up role was a "big challenge" for Gadd.
The actor says that if he were to fail in the role he would "look like a fool" - but he didn't want to let the fear of what people might think stop him.
He had to "change everything" about himself for the role, from growing an "awful beard" to changing his hair and bulking up his muscles.
"I just knew if people were going to buy the guy from Baby Reindeer as this hard-man epitome of sort of masculinity, I needed to really transform," he explains.
A violent altercation at Niall's wedding kick-starts the new series, which cuts between the 1980s and the present day to explore how their relationship fell apart.
Gadd says he was interested in exploring family dysfunction. To do this, he initially establishes Niall and Ruben's bond as "unbreakable, unshakable, for better or for worse".
The pair are forced to live in the same house as teens because their mothers are in a relationship. Ruben solves his problems by fighting while Niall hides parts of himself - and they form an unlikely bond. But secrets and shame start to splinter their relationship which violently unravels.
Both grapple with shame and repression throughout the series - Niall from his sexuality and Ruben from his trauma.
"I think sometimes the things people are most scared of is themselves," Gadd says. "I certainly think in my life I've experienced challenges that have come from repression."
Gadd explains he thought it was interesting to show the two repressed men living in Glasgow, a city that has gone through so much change.
"This city is progressing around [Niall], becoming more vibrant, more colourful, more accepting, and yet he still can't get past his own demons."
Gadd notes that when he was growing up in a small Scottish village, there was an attitude that Glasgow was a "scary" place but that isn't really the case.
Now it's become a "cultural capital of the world" and a "really progressive" place, he says, with a prominent gay community.
While Gadd says he never writes with actors in mind, he couldn't shake the idea of Jamie Bell, who starred in Billy Elliot and Rocketman, playing Niall.
"He's a very celebrated actor, but in my mind, still underrated," he says, adding he felt Bell, set to star in the upcoming Peaky Blinders series, "looked right" for the part.
Ultimately, Gadd is keen for people to make their own mind up about the ending of the series and the characters.
"Whatever they think the ending is, whatever they think the show's about, that's probably what it is."
You can watch Half Man on BBC iPlayer every week from Friday 24 April
