Paul Vasquez, whose ecstasy at the sight of a double rainbow brought joy to tens of millions of viewers on YouTube, died on May 9 at a hospital in Mariposa County, Calif. He was 57.

His death was confirmed on Sunday by the Mariposa County coroner’s office to The Modesto Bee, a local news outlet.

Mr. Vasquez became an internet sensation in 2010 after a video he had posted months earlier on YouTube — a three-and-a-half minute clip in which he enthusiastically observed two concentric rainbows from his California home — was shared by the late-night host Jimmy Kimmel in July.

“Wooo! Oh wow!” Mr. Vasquez shouts in the video before breaking into tears at the double rainbow’s beauty. “It’s so bright and vivid. It’s so beautiful.” Within weeks, the video had garnered millions of views.

“Paul was a catalyst and he made us and the world at large aware of the power of the internet,” his friend Robert Borchard, 76, said in a phone interview on Tuesday. “I never heard the term ‘viral video’ until Paul.” To date, the clip has been viewed nearly 48 million times.

In the weeks following the video’s takeoff, Mr. Vasquez was featured on Comedy Central’s “Tosh.0” and appeared as a guest on “Jimmy Kimmel Live!” Fans created remixed versions of his video, including one by the Gregory Brothers, who used Autotune to turn Mr. Vasquez’s spoken words into a song. The song became available on iTunes, and the Gregory Brothers performed a version of it live in 2011 at VidCon, an online video convention in Los Angeles. Mr. Vasquez was nominated for viral video star of the year at the People’s Choice Awards in 2011.

Mr. Vasquez became so inundated with requests after his video that he hired an agent. He went on to appear in advertisements for Microsoft, Vodafone New Zealand and Smartwater, alongside Jennifer Aniston. He also guest starred in an in-flight safety video for Delta Air Lines.

On Monday, people across the internet expressed grief at the news of his passing. “Rest in peace, Paul,” the YouTube star Tyler Oakley wrote in an Instagram caption of a photo he took with Mr. Vasquez. “Paul L. Vazquez was truly a viral sensation who was so pure of heart & down for the wild & weird ride of the internet.”

YouTube’s head of culture and trends, Kevin Allocca, tweeted that Mr. Vasquez was “one of the most unique people I’ve ever had the pleasure of knowing.”

“10 years ago, a friend sent me a @YouTube video of a man who saw two rainbows in the sky,” Jimmy Kimmel tweeted on Monday night. “This video made everyone happy, as did he. Paul ‘Bear’ Vasquez, the Double Rainbow guy, passed away Saturday. His enthusiasm for life was genuine & the world is gloomier without him.”

Mr. Vasquez was born in 1962 in East Los Angeles. His father, he told CNN in 2015, was a city bus driver, and as a child he explored the city using a free transit pass.

“I’ve always been someone who’s fearless and immensely confident,” he said in the CNN interview.

Mr. Vasquez joined the Los Angeles County Fire Department before moving to Yosemite, a park he had come to know well during his childhood, in 1985. There, he took on various park concessionaire jobs — security guard, emergency medical technician, firefighter — and eventually joined the National Park Service. He also worked as a cage fighter and a truck driver.

For most of his adult life, Mr. Vasquez lived in a small mountainside home just 10 miles from Yosemite park where he grew his own food. But in a March YouTube video, he shared that a tree had fallen on his house in 2019, so he had moved into a small apartment in town. He was a fixture in the community. “Everyone in Mariposa is connected to Paul in some way,” Mr. Borchard said.

Mr. Vasquez married once; the relationship ended in divorce. He is survived by two children, a daughter, Irene, and a son, Paul.

In the decade following the “double rainbow” video, Mr. Vasquez continued to post frequently on YouTube. He also shared status updates on Facebook, including a post on May 5 in which he divulged that he was sick and being tested for Covid-19. “I’ll get my results in two days, however at this point I’m fairly certain that I don’t have it,” he wrote. “I didn’t have a fever. Something else is going on with me.” Days later, he died in the emergency room at John C. Fremont hospital in Mariposa, the Modesto Bee reported.

Mr. Vasquez is best known for his love of rainbows (“You can’t look at a rainbow anymore and not think about me,” he told CNN), but he used his platform to share his appreciation of nature at large. He showed viewers how he grew his crops, caught and released rattlesnakes and grew wildflowers in his yard. His fame didn’t make him rich — according to CNN, Mr. Vasquez was only making $6,000 per year in 2015 — but he said that he was able to keep costs low by living off the land.

“Helping our culture reconnect with the world around us, that’s what his videos were about,” Mr. Borchard said of his friend. “Our urban lifestyle is disconnecting us from nature. Paul was trying to reconnect us. That’s his legacy.”