Once dismissed and widely ridiculed as music for pensioners, trot blends traditional Korean music with elements of Western jazz, swing and Japanese Enka.
But 33-year-old Lim is one of a fresh crop of younger artists breathing new life into the genre, with its melodramatic ballads and upbeat tunes finding massive audiences in the South, helped by a wave of reality television shows.
The original and most successful of these, "Mr Trot" was won by Lim in 2020, with more than a third of all South Korean viewers watching the final -- and his victory turned him into a nationwide sensation.
His songs now have a record-breaking 10 billion streams on Melon, the South's largest music platform; his official fan club has more than 200,000 members; and his stadium tours sell out in minutes.
Lim is also South Korea's most loved singer, according to a June Gallup poll, beating out BTS, who were ranked third favourite at home.
He also out-earns BTS members -- individually, not as a group -- with ticket sales for his recent tour raking in about $22 million, industry data shows.
"Domestically, articles about him generate more traffic and gain more likes than BTS," veteran entertainment journalist Seo Byung-ki told AFP, adding this was known as "Lim Young-woong syndrome".
The star's moving back story -- "losing his father at a young age, growing up with the care of his grandmother, barely making a living, then winning a television show" -- coupled with his "perfect" vocals make him a surefire public hit, Seo said.
Although he's largely unknown internationally, his fame has spread to the isolated North, where music from the South is banned, but activists routinely send USB sticks full of his songs by balloons across the border. Defectors have reported he's popular.
- Elderly fans -
At a recent concert in Seoul, tens of thousands of fans, all dressed in sky blue and waving glowing electronic wands, wept as Lim appeared on stage.
His fans are mostly elderly, and for many, this is their first celebrity obsession.
Baek Soon-ok, 87, had never watched a YouTube video of a celebrity or attended a concert before she discovered Lim.
"He's such a kind person, good to his mother, and most of all, a great singer," she said, wearing a sky-blue T-shirt with Lim's face.
"I never imagined I would like an artist as much as him," she added.
In Lim's hometown of Pocheon city, a sky-blue cafe named "Woong's Tree" doubles as a shrine to the singer.
Outside, the walls and windows are adorned with photographs of Lim. Inside, an extensive collection of his merchandise is on display, alongside life-size, smiling cutouts.
Lim "saved her life", cafe owner Chun Eun-kyung told AFP, saying that when she was diagnosed with breast cancer, his music helped her endure treatment.
"I listened to his song 'Wish' when I was in chemotherapy and it struck my heart," she said, adding he helped her let go of her fear of dying of cancer.
After that, she began to follow Lim wherever he performed, and along the way, she met fellow super fans -- known as Hero Generation, as his name means "hero" in Korean -- and opened the cafe to create a space for them to gather and celebrate Lim.
"He's my strength, my happiness," said another fan and cafe regular, 60-year-old Lee Bu-duk.
Trot prodigy
Although K-pop still dominates South Korea's musical exports with artists like NewJeans topping US charts, local credit card data suggests trot is growing faster domestically, with K-pop concert sales up just 34 percent, compared to 134 percent for trot.
And more young singers are entering the market. Lim and his "Mr Trot" appearance made Park Sung-on -- then just 12 -- realise he wanted to pursue the genre.
"I think it fits the sentiment of what Koreans feel," Park told AFP of the genre.
He appeared on a later version of the "Mr Trot" show and finished in the top 10.
Now hailed as a budding "trot genius", Park released his debut single in March 2023.
"I don't think I'm a star. I had to work hard to get here," he said.
But Park says he hopes to dedicate his life to trot. "I think of it as a lifelong partner."
