Jessica Gunning has always played the 'comic relief character'. Then she was offered Martha.

In the two weeks since the limited series Baby Reindeer hit Netflix, it has totally and unequivocally placed the world in a chokehold. It arrived with little fanfare but as it quickly found an audience, we all became transfixed by this gut-punch story which is based on true life events.

When it comes to what makes for a successful TV show, often it's hard to pinpoint exactly what the secret sauce is. It could just be kismet (you know, hitting the public at just the right time) — but for Baby Reindeer, there are two things that make it one of the best shows we've seen in recent history.

Watch: Baby Reindeer official trailer. Story continues below.

Firstly, it's hard not to go past the fact that this series is based on the very real events that took place in comedian Richard Gadd's life. Like many banging scripted shows, the source material of real life will often make for a pretty compelling story. His encounter with a stalker and the abuse he suffered at the hands of a mentor has made for a haunting watch.

Secondly, Baby Reindeer has just been so bloody well cast. From Gadd playing a version of himself (in what must have been no easy feat) as Donny Dunn to breakout star Nava Mau (playing Teri), this chorus of talented actors has given the series the heart, soul, pain and depth needed to pull off such delicate subject matters.

And then there is Jessica Gunning who plays Donny's stalker Martha Scott. At any given moment, her range swings from terrifying to terrified, and gathers all the nuance of a woman dealing with severe mental health issues with one hollowed stare. 

Her portrayal of Martha, in a word, is simply mesmerising. 

It would've been all too easy to portray Martha in a caricature of what we're led to believe a stalker looks and sounds like. Gunning's version brings dimension and humanity to a troubled person.

"I really cared about Martha, you know," she told BBC when speaking about her process in becoming the character.

"As soon as I read episode one I was drawn in by her. I never saw her as a villain. I don't think you can if you're playing that kind of part."

When it came to casting Martha, Gadd knew they had to get it right. 

"What I needed to see was the essence of the person, the kind of energy, and no one did it like Jess. She’s phenomenal," he told Variety. 

"I needed to see someone who was vulnerable one moment, angry the next, volatile but so desperate and sympathetic."

Jessica Gunning as Martha in Baby Reindeer. Image: Netflix.

Gunning says that of all the characters she's played before, saying goodbye to Martha was challenging especially given how personal this project was for Gadd.

"Even when there were days I wasn’t in, I was thinking of Martha and the story, just wanting to do the best I could do," she said in an interview with Metro. 

"In that aspect, I didn’t really let go of her until we finished filming. I couldn’t really put her to bed. When you do a job like this as well, it’s long hours, and you’re there, and you’re in it. With this, emotionally, everyone was really invested — it does dominate your life — it took a while to, kind of, say goodbye in a way. I was really sad when it finished, to say goodbye to her."

Having worked in the entertainment industry for 17 years, Gunning is no overnight success.

She most recently starred in the comedy The Outlaws, a series about a group of misfits banding together to complete community service. Acting alongside Stephen Merchant and Christopher Walken, Gunning showed off her prowess for timing and satire.

She has largely found steady success in the UK, appearing in shows including  Fortitude, In The Dark, Jericho and Top Coppers, but with the release of Baby Reindeer, she has reached international recognition.

After an almost two-decade run in the industry, Gunning knows that it was all leading up to this point.

"I can do many a job," she said in an interview with BBC. "But I feel Martha is kind of the role of a lifetime."

The pipeline for breakout actors who find themselves in the zeitgeist of a hit Netflix show often leads to other exciting projects and Hollywood knocking on the door. But for now, Gunning is quite content basking in what has been an immensely meaningful project.

"I don't think of Baby Reindeer as a springboard for anything, or a moment," she told BBC. "I just feel genuinely so proud to be part of it and I'm so proud that so many people are having such a response to it."

Feature Image: Getty/Netflix.