In the final Calvin and Hobbes comic strip, published Dec. 31, 1995, Calvin and his tiger pal Hobbes step out into a fresh coat of snow, sled in hand. “Everything familiar has disappeared! The world looks brand-new!” Hobbes remarks. The last panel of the strip shows the pair sledding down a clean white slope, dust and scarf tails flying behind them, as Calvin dispenses one last nugget of joie de vivre: “Let’s go exploring!”

Joel Allen Schroeder, director of the documentary Dear Mr. Watterson, has done a lot of thinking these past few years about that final strip and its creator, Bill Watterson.

“Just the concept of ‘Let’s go exploring,’ I think that’s a motto for living, a way of life,” Schroeder says.

The famously shy Watterson does not make an appearance in the film, and Schroeder doesn’t even make an attempt to track him down.

Instead, the film takes exactly the form the title would suggest: A fan letter.

Visually, the documentary includes many headshot interviews, a few romps into museums and libraries, and a lot of panning shots of comic strips. Viewers are reminded of the charm and wide-eyed wonder of the series; references are made to neighborhood snowball fights, Spaceman Spiff, and the cardboard box that Calvin fashions into a Transmogrifier. Schroeder says he hopes that, if nothing else, the film will encourage people to dust off their old Calvin and Hobbes anthologies and give them another read.

The first act feels more or less like fan art, with everyday people gushing about how much they love the comic and how they would have given a limb to have a Hobbes doll growing up. It’s sweet, but it gets cloying.

The documentary really picks up when Schroeder starts interviewing other comic artists about Watterson’s style, influences, and philosophy. It turns out that many of Watterson’s contemporaries have elaborate theories about the man behind the pen, despite the fact that many have never spoken to him. As Bizarro creator Dan Piraro remarks, Watterson is “the Sasquatch of cartoonists.”

Watterson is the polar opposite of commercially savvy comic artists like Jim Davis (Garfield) and Charles Schulz (Peanuts), who have broadcast their art on coffee mugs, calendars, TV shows, insurance commercials, and Thanksgiving Day parade floats. While neither artist appears in the documentary, Schroeder does land a revealing interview with Bloom County creator Berkeley Breathed, who has made his share of licensing money on Bill the Cat and Opus the Penguin dolls.

As it turns out, Breathed traded a series of letters with Watterson, often accompanied by personal comics written for each other’s eyes only. He holds one up for the camera in which Watterson has caricatured Breathed, showing him stuffing wads of cash into the engine of a speedboat.

Schroeder interprets Watterson’s business decisions as a kind of purist anti-materialism. “If Calvin or Hobbes said something in the strip, he didn’t want those things to be watered down by something Calvin might say or Hobbes might say about a product,” Schroeder says.

The film also comments on the high-vs.-low-art dichotomy, the evolution of Watterson’s style, and the decline of the newspaper comic section. Schroeder admits early on that he’s not a comic strip expert — just a fan. But he makes up for it with research, including a trip to Watterson’s idyllic hometown of Chagrin Falls, Ohio. “You’ve got the woods, the open landscapes, and the hills. It looks like Calvin and Hobbes, and it looks like home for me,” says Schroeder, a Wisconsin native now living in Los Angeles.

For many diehard Calvin and Hobbes fans, the end came too soon in December 1995. Watterson sent a note to newspaper editors, explaining, “I believe I’ve done what I can do within the constraints of daily deadlines and small panels.”

Over the six-year process of making the documentary, Schroeder says he came to understand Watterson’s motivations a little bit better.

“Looking back, we have that one decade, those perfect 10 years of the strip, and if it was 20 years of the strip — the complete collection is big enough as it is, right? The three volumes are heavy enough to demonstrate the heft and the value of it, but not too overwhelming,” Schroeder says.

Much of Dear Mr. Watterson is speculation, more or less, since no one (or almost no one) has spoken to Watterson. What Schroeder does know is that the artist has at least seen the documentary.

“What we know for sure is he has said that he appreciated the choices that we made to make it less intrusive,” Schroeder says.

At the very least, we know Watterson has a sense of humor about his career. When Mental Floss landed a rare interview with him for the magazine’s December 2013 issue, the writer asked him for his thoughts on all those unlicensed window decals of Calvin peeing on various logos and symbols.

Watterson’s answer: “I figure that, long after the strip is forgotten, those decals are my ticket to immortality.”

That and a lovingly made documentary and a treasure trove of anthologies on coffee tables and bookshelves around the globe.