These days, Disney’s “The Little Mermaid” has frequently found itself in the crossfire for being behind the times, whether for the fair criticism that it extols a girl who sacrifices her voice to be with a man she just met or the outrageous backlash that greeted the casting of a black actress for the lead role in an upcoming live-action remake.

“The Little Mermaid” began by turning the prim and deferential nature of the fairy tale princess on its head.

The din can obscure the fact that the animated classic was revolutionary when it debuted 30 years ago Sunday, both for the agency and spunk it gave its female cast and for the way it both revived and redefined the animated Disney musical. Indeed, today’s Disney musicals — the multi-billion-dollar juggernauts of screen, stage and merchandising — don't exist without “The Little Mermaid”; the genre had been languishing for decades until it arrived.

Walt Disney Studios was in crisis before “The Little Mermaid” came along in 1989. As chronicled by Chris Pallant in “Demystifying Disney: A History of Disney Feature Animation,” the company had lost direction following the deaths of Walt Disney and his brother Roy more than a decade earlier. Films produced in the early 1980s such as “The Fox and the Hound” emphasized cost-cutting over innovation, sapping morale and quality. Meanwhile, high-level Disney defectors in 1986 succeeded in making an animated movie, “An Americal Tail,” that outperformed Disney’s that year.

For the first time in half a century, Disney was no longer the dominant force in animation. Floundering, the company placed its hopes on a story that was originally planned for release in the 1930s but never ran: “The Little Mermaid.”

Disney had recently received an injection of fresh blood in the form of CEO Michael Eisner and chairman Jeffrey Katzenberg. The pair were willing to experiment and attempt more ambitious projects, including returning to the complex and more expensive animation of the past. They tapped promising animators Ron Clements and John Musker to co-direct a fairy tale musical updated for a new generation with the goal of revitalizing the animation division.

“The Little Mermaid” succeeded in this mission and then some. In modernizing the treatment of female characters while harnessing the power of the Broadway musical form and upgrading its animation technology, it became the model for future Disney films. The result was a decade of box-office triumphs that re-established the company as the dominant force in American animation — and arguably in many households via retail goods and cultural touchstones.

“The Little Mermaid” began by turning the prim and deferential nature of the fairy tale princess on its head. The protagonist, Ariel, is defiant of her father’s authority, driven by love and excited to go on an adventure. While today Ariel would not be considered a progressive heroine, she was far more proactive than previous female Disney leads, who spent much of their movies waiting to be rescued. Instead, Ariel first meets the prince Eric when she saves him from drowning.

This step forward faced some resistance, however, as Katzenberg was skeptical of the box office viability of a “girl’s film.” But critics and audiences loved the movie. Prominent critic Roger Ebert praised Ariel as an active and rebellious heroine. Her influence can now be seen in everyone from Belle in “Beauty and the Beast” to Jasmine in “Aladdin” to Mulan in “Mulan.”

Similarly, the antagonist of the movie, Ursula, reinvented Disney villains. Unlike no-nonsense evildoers of the past, Ursula is the most flamboyant character in the movie — and another strong woman who dominates the screen. Rather than using traditional fairy tale representations, she was based off the drag queen Divine. The directors took several actresses to get to the perfect choice: Pat Carroll, whose rendition of a theatrical villain-cum-aggressive salesperson was immediately acclaimed as one of Disney’s greatest villains. Jafar from “Aladdin” and Scar from “The Lion King” are just two of her protegees.

These forceful screen personas were also for the first time given music that enabled them to fully realize their characters and narrative potential. The most critical moments of plot and character development in “The Little Mermaid” are told in song, in contrast to earlier Disney songs such as “Bibbidi-Bobbidi-Boo” from Cinderella that were meant to be bright and entertaining in isolation.

Both producer and songwriter Howard Ashman and composer Alan Menken had backgrounds in musical theater and applied the conventions of the stage to animation. The classic song “Part of Your World” is an archetypal example of a Broadway “I Want” song, where the protagonist sings about their desires and motivations, and is rendered by Ariel complete with a stage-like spotlight on her.

This innovation at first faced resistance, too. When an unfinished version of the film was screened for a test audience of children, the kids seemed bored during the song and Katzenberg wanted it cut from the film. The directors insisted it was essential. Now Disney animated musicals almost invariably feature these anthems, from “I Just Can’t Wait to be King” in “The Lion King” to “Let it Go” in “Frozen.”

“The Little Mermaid” was also the first movie to begin to combine characters in the foreground with scenery in the background digitally. This innovation allowed animators to incorporate computer-generated graphics into their movies, greatly increasing animation quality and efficiency. The Computer Animation Production System the moviepioneered went on to be used for more than a decade.

“The Little Mermaid” was a huge gamble for Disney. With a production budget of $40 million, it was one of the most expensive animated movies ever made at that time. But it was a wise wager: The box office returns it reaped were replicated many times over in future Disney movies. The studio’s most recent hit, “Moana,” was directed by the same Clements and Musker duo who revolutionized animated movies 30 years ago.