The Frates family decided that Saturday’s eighth dive into the frigid waters off nearby Good Harbor Beach would be the last Plunge for Pete, a fund-raiser they began in 2012 after his diagnosis of ALS, also known as Lou Gehrig’s disease, and one of many events organized or endorsed by the family that has helped raise many millions for ALS research. For Pete’s widow, Julie, who stood by him through his painful physical decline, it was also her first plunge.

Pete Frates used social media to help popularize the “Ice Bucket Challenge,” a viral Internet sensation that inspired an unprecedented outpouring of support for ALS research — more than $220 million worldwide, according to the ALS Association.

During his illness, “We grieved every day,” Nancy Frates said.

“We would wake up every morning and wonder what part of Pete we would mourn that day,” she said. “There were the major milestones of when he would go into a wheelchair or when he couldn’t talk anymore, but there were little milestones: the day he couldn’t text anymore, the day he couldn’t drive anymore. People don’t understand the magnitude of these things that we all take for granted that were slowly taken away from him.”

More than 1,000 people showed up Saturday to support the Frates family and remember Pete, and hundreds ran into the icy waves, many costumed as wildlife such as a reindeer, a duck, or a shark, or as cartoon characters or celebrities.

Among them was Michael Spicer, 34, of Wellesley, who wore tight jeans, a sleeveless undershirt, and a dark mustache for his portrayal of Freddie Mercury, the late lead singer of Queen.

Spicer, who was Pete Frates’s roommate at BC, said he has done the plunge since the start, and “every year I just try to one-up myself. . . . I always try to pick out something clever and easy — and cheap.” In the past, he has dressed as KISS lead singer Gene Simmons, the character Maui from the animated film “Moana,” and one of the Village People.

“Pete really liked music; he was a rock and roll guy,” Spicer said. “Maybe not a huge Queen fan, as much as I am. He was a big Led Zeppelin guy, but I wasn’t about to dress as Robert Plant.”

Spicer remembered his friend as “one of the kindest, nicest guys out there” and someone who never gave up. “I miss him dearly, but he’s in a better place now, and he can be himself again. And he changed the world.”

Sisters Erin Barker, 26, and Ali Barker, 23, both of Danvers, were dressed as Mermaid Man and Barnacle Boy, characters from the cartoon “SpongeBob SquarePants,” whose creator, Stephen Hillenburg, died last year of heart failure caused by ALS.

The Barkers, who have been coming to the dive since it began, have an aunt and uncle who are close with the Frates family, they said, but they were also paying tribute to Hillenburg and to their grandfather, who died of ALS.

“It’s very meaningful for us,” Erin Barker said. She wore a swimsuit top she had worn for the first plunge in 2012; across it was written, “I’m plunging for Pete, in loving memory of Grampy.”

As the sisters dried off on shore, both said they didn’t mind the cold water. “I just run for it,” Ali Barker said. “I don’t even think about the cold.”

Julie Frates, Pete’s widow, took the plunge for the first time, wearing the same red, white, and blue bikini she wore the day she met him at a Marblehead beach on the Fourth of July 2011.

Throughout the day, she was surrounded by a bevy of female friends; one carried a poster that read, “Julie’s Hype Girls.” Those friends were right beside her as she led the mad dash into the cold Atlantic waters.

As they emerged, Frates said she felt “great,” and she credited her friends with helping get her through the last three weeks.

“These are my ride-or-dies. These are the ones that made me do this,” she said. [They] actually just got me out of bed and put some clothes on me. . . . It’s devotion, and it’s really undying friendship.”

It was moving, she said, to see the huge crowd and to dive into the waters with them for the first time.

“Pete gave me the perfect weather,” she said, “so I couldn’t really refuse.”

Jeremy C. Fox can be reached at jeremy.fox@globe.com. Follow him on Twitter @jeremycfox.