The multi-talented writer and performer first introduced viewers to Ja'mie in his breakout hit We Can Be Heroes before bringing her back for an encore in Summer Heights High.
Now she's taking centre stage in a series of her own, the new six-episode comedy Ja'mie: Private School Girl, which sees the self-absorbed teenager in her final year of high school.
Everything seems to be going Ja'mie's way - she's school captain, lording it over friends, family and enemies alike, and even appears to have found a hot boyfriend, albeit one who's a couple of years younger than her.
"She kind of goes up a notch with this series," Lilley says.
"And with everything that's going on, it's a lot more adventurous this time around."
Still, there's every chance the turbulence of adolescence, not to mention her own tendency towards narcissism and nastiness, may be Ja'mie's undoing.
In his previous three mockumentary series (which includes last year's ambitious Angry Boys), Lilley has played multiple characters of various races and different genders.
But Ja'mie: Private School Girl marks the first time he's focused solely on one character. Surprisingly, that may have posed even more of a challenge than usual for Lilley.
"I think at first I thought it would be a bit of a walk in the park," he admits.
"I'd just done Angry Boys, which was kind of epic with its five different characters, so I thought this would be a breeze. But I had just as much screen time to fill, and Ja'mie is in every scene, so there was even more pressure on the character.
"You know, I couldn't just go, 'Meanwhile' and cut to another character. So I didn't find it easier. But I like things to be challenging."
And bringing Ja'mie to life is a challenge, according to Lilley. He's admitted to interviewers that he finds it "awkward" portraying a teenage girl. But placing her in the spotlight was a move he couldn't pass up.
"I was excited by the opportunity to do a show purely about one character and I was excited by this character," he says.
"I've dabbled in her world so much on We Can Be Heroes and Summer Heights High, and that sort of planted the seeds for a lot of little things that I thought would be fun to revisit and expand on."
Expanding Ja'mie's world and depicting it accurately required research, though, and Lilley did his due diligence.
"A lot of what they say and do is taken from Facebook and television and things I see going on around me," he says.
"But I also arranged through friends to meet with groups of girls and talk to them about it. People are excited by the idea of being part of it but I found they liked to tell me what to do - some thought I was there to get their ideas. 'No, you guys just talk and I'll observe'."
During his observations, Lilley found "teenagers always like to think they're the first people ever to be teenagers".
"I was speaking to one girl who said she and her friend have been saying, 'Oh my God' a lot," he says.
"I thought, 'Really? Well, that's original'."
He may have a sharp eye for the flaws and foibles of his characters, especially Ja'mie, but Lilley nevertheless has affection for them.
"I think you like to be entertained by Ja'mie and I think you like to watch her fail sometimes. But I think you do like her," he says.
"It's the classic documentary thing: she wants to appear a certain way but she's being exposed as something else. And she's perfect for that because she loves to put herself out there and talk about herself, and then you can go, 'Wait a minute, what's really going on here?'
"But I think if you were a teenage girl and she didn't target you and pick on you, you'd be pretty happy to be her friend. You'd feel hot by association - 'She chose me!'.
"So, yeah, I think you do like Ja'mie. I like her."
- AAP
