A Lena Dunham tattoo is an unlikely impetus for a documentary, but that's exactly what we have in "It's Me, Hilary: The Man Who Drew Eloise," which screens on HBO Monday night (9 p.m.).

The documentary, produced by Lena Dunham and directed by Matt Wolf, delves into the life and career illustrator Hilary Knight, most famous for drawing the "Eloise" books, about a mischievous 6-year-old girl who lives at the Plaza Hotel.  

The film looks at Knight's fun and fantastical world and explores the impact of the falling out between Knight and "Eloise" author Kay Thompson.  

After becoming friends when word got to Knight that the "Girls" star and creator had a tattoo of Eloise on her back, Dunham suggested to filmmaker and friend Matt Wolf they make a film about Knight's wonderland Upper East Side apartment, full of autobiographical objects, images and drawings.  

The documentary soon evolved, Wolf told amNY. "I did a little digging, and I found great 1950s archival footage of Kay Thompson from the Eloise era ... It made us realize that there was a bigger story that we could tell and that started to really conceptualize the film."   

In addition to archival footage, the 88-year-old Knight, an avid home moviemaker, had a wealth of footage he'd collected over decades. "It was sort of like a documentary filmmaker's dream," Wolf said. It felt like 'oh it's possible for us to dive into the past and really tell the story that covers the full life's work of Hilary.'"  

The influence "Eloise" has had on generations past and present demonstrates the book's firm place in Americana. As well as conversations with Dunham, women including Mindy Kaling, Tavi Gevinson and Fran Lebowitz appear in the documentary to share their thoughts on the character.  

"There's a timelessness and universality to Eloise's character," Wolf said. "Lena and I really thought of Eloise as this proto-feminist icon and I think that the way that she doesn't care about how she looks, she's kind of slobby, but also super willful and sassy … I think those kind of characteristics resonate with little girls, and also little boys who don't fit into the typical mold and who are rebellious by nature." 

Knight's twin nieces, Lily and Kitty, also speak about their uncle, with whom they are now collaborating on graphic novel titled "Olive and Oliver," about twins separated at birth. 

Knight told amNY in an interview last week that he thought the film has turned out wonderfully and praised Dunham for her work. "It's all Lena, it was her idea and she made it happen, and I'm indebted to her ... to have someone as brilliant as she is. We will have Lena Dunham longer than Eloise. I am sure of that."