Pickle Rick. Get Schwifty. Wubba lubba dub dub. Those phrases may not strike a chord with you. But, for TV viewers of a certain age (adults between the ages of 18 and 34, for instance), they should be instantly recognizable from the Cartoon Network/Adult Swim animated series, Rick and Morty: millennials’ favorite TV comedy.

Currently in its third season since debuting in 2013, the show is part intergalactic adventure, part family comedy, led by a brilliant but caustic (and alcoholic) scientist, Rick, and his relatively average teen grandson, Morty. Stacked deep with pop culture references and absurdist nihilism, Rick and Morty doesn’t seem like a safe bet for broad appeal on it surface.

But, overall viewership for the current season is up 81% over the previous season, and the series is the number one comedy on TV so far this year in the coveted demographics of adults 18-24 and adults 18-34, based on Nielsen ratings that track live viewership plus streaming and on-demand viewing over an initial week-long period. By that measurement, Rick and Morty is outpacing award-winning broadcast TV shows like CBS’ The Big Bang Theory and ABC’s Modern Family with younger viewers this year.

Christina Miller, the president of the Time Warner-owned Cartoon Network and Adult Swim, told Fortune that Rick and Morty goes beyond just appealing to millennials, though. Based on recent ratings, more than 2.5 million people overall are likely to tune in for the current season’s finale, which premieres this Sunday night at 11:30 pm ET. Those are especially impressive results for an animated show that’s definitely aimed at adults (most episodes feature adult language and animated violence), much less one that airs so late on Sunday nights. Those numbers also suggest that people of all ages are watching the show, and Miller thinks the audience will only grow more.

“I do think more people will come to it,” Miller said. “But, more importantly, they’re staying with it, and that’s been the difference-maker.”

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Indeed, Rick and Morty’s early fans exercised no small amount of patience over the nearly two-year period that lapsed between the end of the show’s second season and the current season’s official return over the summer. In the world of “Peak TV” and countless entertainment options, two years is a long time to stay excited and engaged with a TV show.

And, yet, instead of hurting the show, though, Rick and Morty returned from its long absence with a stronger viewership than ever. First, the show briefly returned to TV in an April Fools Day stunt, when Adult Swim surprised fans by streaming the first episode of Season 3 online in a constant loop for four hours on April 1. The streams pulled in 3 million unique visitors, while a similar livestream hosted on Facebook got 8.7 million video views. (The show’s social media following is also very strong and active, with more than 2.8 million followers on Facebook, plus more than 1 million on Twitter and 1.6 million on Instagram.)

When the series finally returned to cable, on July 30, 2.86 million people tuned in for the Sunday night premiere, according to Nielsen, making it the night’s second most-watched cable program, behind HBO’s ratings monster Game of Thrones (9.2 million). The most-watched episode before this year was Season 2’s second offering, “Mortynight Run,” with 2.19 million total viewers.

Last week, the show’s penultimate episode of the season pulled in just under 2.5 million total viewers (1.9 million of whom were between the ages of 18 and 49). The episode was the most-watched cable show on that Sunday night, beating out a new installment of AMC’s Fear the Walking Dead, and making Rick and Morty cable’s most-watched non-sporting event of the week for viewers between 18 and 49.

Another indicator that Rick and Morty‘s footprint ascended to a whole new level with the current season is the fact that a reference to a long-discontinued McDonald’s condiment (Szechuan McNugget sauce) in the season’s first episode resulted in a fan-driven online campaign to resurrect the sauce (McDonald’s even responded by sending some of the sauce to the show’s creators). “To me that’s just an example of Rick and Morty driving pop culture more than anything else,” Miller said.

One reason for the uptick in viewers could be that the show needed time to grow its audience, with the earliest, most die-hard fans building hype via word of mouth. It also helped that co-creators Dan Harmon (Community) and Justin Roiland spent that time engaging with fans on social media—interactions that sometimes found the two writers and voice actors having to assuage anxious fans’ concerns that the new season was delayed because of personal difference between the two men and that Rick and Morty might never return.

But, Miller and her team at Adult Swim also used the show’s time off the air as an opportunity to get a lot of mileage out of the types of ancillary content and fan events that typically accompany the marketing-heavy period that comes before a popular show returns to the air. During that time, fans of the show could keep up with the Rick and Morty comic book series that first launched in April 2015, while a roving pop-up “fan experience” featuring a vehicle shaped like the character Rick (aka the “Rickmobile Tour“) attracted huge crowds in 40 U.S. cities over the summer, with fans lining up to buy merchandise from the show.

Meanwhile, in April of this year, Adult Swim’s gaming arm launched a virtual reality video game for HTC Vive and Oculus Rift, called Rick and Morty: Virtual Rick-ality, which became the most-downloaded game for the day it debuted on online game store Steam. And, over the summer, the network released an online multiplayer video game, called Pocket Mortys, where users compete to collect various incarnations of the Morty character from the show.

Looking ahead to the next layoff between seasons (the network already ordered a fourth season, and creators Harmon and Roiland have hinted it could have more than the show’s usual 10 episodes), Miller said Rick and Morty fans will have no shortage of comic books and Pocket Mortys (the game has 13.1 million downloads to date) to pass the time.

Miller said that the extra content kept fans energized about the show and helped bridge the gap between seasons. “In order to be a so-called modern hit, you always have to be on,” she said, referring to the show’s multi-platform approach that allows fans to find no shortage of content related to the show even when it’s off the air. “The way people experience entertainment and content has changed a lot,” she added. “People expect for it to be dynamic, and when you can do it, and do it well, I think you can build a success like this.”