With more than 11 million copies sold, the kooky country Christmas classic that is "Grandma Got Run Over By a Reindeer" is a musical gift that keeps on giving—and that can evidently never be returned. It’s the fantastical tale of a tipsy old lady who’s trampled to death by Santa’s sleigh, and the story behind the song is nearly as good.

It begins, like all Christmas fables should, with a blizzard. It was December 1978, and a San Francisco veterinarian named Elmo Shropshire, a.k.a. Dr. Elmo, was booked at the Hyatt in Lake Tahoe with his then-wife, Patsy. The couple had a comedy-bluegrass duo called Elmo & Patsy, and just before taking the stage, they got a visit from one Randy Brooks, a Texas singer-songwriter who’d played the hotel before them and gotten stuck there by the snow.

"I was never what I’d consider to be much of a singer," Dr. Elmo tells mental_floss from his home in California. "I always sang novelty songs, so it didn’t matter if I could sing or not. At the time, we were doing a lot of funny songs. Randy saw our show and said, 'I’ve got this song I think would be perfect for you.'"

The song, of course, was "Grandma Got Run Over by a Reindeer," which Dr. Elmo deemed "the most original take on Christmas music" he’d ever heard. "I didn’t know how long it would last," he says. "But I knew it would get people’s attention the first time he sang it."

Funnily enough, "Grandma" didn’t get much of a reaction from the audience at the Hyatt, where Elmo & Patsy played it with Brooks the night they met. "They thought it was kind of cute," Dr. Elmo says. "There are some songs that are more in your face than that one. The song has all the trappings of Christmas in it, except for that one thing."

That one thing—the old woman getting blindsided by St. Nick, plus the indifferent response from her family—made all the difference. In 1979, an early recording by Dr. Elmo found its way to influential San Francisco DJ Gene "The Emperor" Nelson, who made it a local sensation. Then December 26 rolled around, and Dr. Elmo figured the fun was over. Not even close.

"The following year, word spread from radio station to radio station," says Dr. Elmo, who wisely secured the publishing rights early on. "This wasn’t anything that started out with any big-time radio hype. We weren’t giving DJs cocaine or women or anything. I didn’t have the wherewithal to do all that stuff."

Dr. Elmo self-released 500 copies on 45 rpm vinyl, and by 1981, as the buzz continued to build, he dared to think bigger. In 1982, a company in Nashville contacted him about pressing up 250,000 copies. Dr. Elmo feared he’d be stuck with a garage full of unwanted product, but the records flew off the shelves like Santa’s caribou. That’s when he decided to sell his veterinary hospital to finance a music video, which he shot for $30,000 at his home. At this point, he still didn’t have a record deal.

"After I made the video, I had what you’d call filmmaker’s remorse," Dr. Elmo says. "I paid all that money, and nothing was happening. The 250,000 copies was a good sell, but we didn’t make any money—not enough to pay for the video."

But the investment soon paid off. In November 1983, Dr. Elmo got a call from MTV. The network loved the clip, and it’s easy to see why. Although Grandma lives in the end—a happy ending Dr. Elmo figured was necessary to sell the thing—the video has a vaguely subversive, charmingly low-budget quality that was bound to appeal to teenagers. In the last week of the Christmas season, with the vid in heavy rotation, "Grandma" passed Bing Crosby’s "White Christmas" on the Billboard holiday charts.

"My father would’ve rolled over in his grave," Dr. Elmo says with a laugh. "He thought Bing Crosby was the greatest singer in the world. And so did I."

As Bing felt the sting of the public’s changing tastes, Dr. Elmo was finally in a position to make some money. In previous years, every record company he’d queried had mailed back his letter with the same message: "Stop sending us this crap." With his crap now smelling like gingerbread, Dr. Elmo flew to L.A. and signed a deal with Columbia Records. The label reissued the full-length Grandma Got Run Over By a Reindeer album he’d recorded the previous year, and in December '84, the LP became the label’s top seller, outpacing Michael Jackson’s Thriller, which was two years old but still plenty popular.

In the 30 or so years since, Dr. Elmo has basically become the Michael Jackson of novelty holiday tunes about hilariously slain matriarchs. Despite the occasional protest from groups like the Gray Panthers, who once gave Dr. Elmo a major publicity boost by labeling the lyrics sexist and ageist, "Grandma" returns each year to leave hoofprints on the popular imagination. The perennial radio favorite has spawned numerous commercial tie-ins, including a 2000 animated TV special and a line of Hallmark musical greeting cards, buttons, and an ornament. This year, fans have their pick of "Grandma" hats at Shopko and dozens upon dozens of apparel options at Walmart.

According to Dr. Elmo, there are even plans for a full-length feature film, so clearly, the franchise still has legs. And so does Dr. Elmo. When he’s not singing his holiday jam, the 80-year-old can be found outrunning the competition at senior track meets and road races. In 2005 at age 69, he finished the New York City Marathon, and in 2013, as a member of Team USA’s 4x400 relay, he won a gold medal at the World Masters Games in Porto Alegre, Brazil. On the day he spoke with mental_floss, he was gearing up for the Florida Senior Games.

Win or lose, he’ll probably be the only participant able to say he’s shared bills with Gwen Stefani and Avril Lavigne and rocked with The Roots on The Tonight Show With Jimmy Fallon. For a one-hit wonder, Dr. Elmo has had a remarkably fruitful career—one that likely wouldn’t be possible today. As he says, "Grandma" went viral at a time when major labels still mattered and radio stations were the source of new music. With everything moving toward streaming, it’s harder for any single artist or song to really capture the public’s attention.

"Everyone just listens to whatever they want to hear now," Dr. Elmo says. "That’s the difference. That’s both good and bad. If you’re a person who likes music and likes to listen to what you want to hear, there’s never been a better time."

As for why people still dig "Grandma," Dr. Elmo says it continues to fill a void in the holiday music market. "All those hits from the early '50s were really sweet and wonderful and lovely," he says. "They liked to play them in shopping malls so people would buy stuff. When this song came along, another generation of people—and even the younger generations now—embraced it because it’s a little dark. It was much more to their sense of humor. It wasn’t too syrupy sweet."

The song’s darkest moment comes in the second verse, where Grandpa responds to his wife’s death by swilling beer and watching football, like nothing happened. There are two possible ways to read his reaction: Either the old man is coping as best he can, or he’s quietly relishing his newfound freedom. Dr. Elmo is a veterinarian, not a psychologist, but he has a theory.

"He was just kind of tired of the old woman," he says with a laugh. "Grandpa is old. He likes to drink beer and watch football. That’s it."