Walter Mondale, who transformed the role of U.S. vice president while serving under Jimmy Carter and was the Democratic nominee for president in 1984, died Monday at 93, according to a family spokesperson.

The big picture: President Biden, who was mentored by Mondale through the years, said in 2015 that the former vice president gave him a "roadmap" to successfully take on the job.

He was the first vice president to have an office in the White House and was deeply engaged in both U.S. and foreign policy, working closely with the president.

"I took Fritz's roadmap. He actually gave me a memo, classic Fritz, gave me a memo, as to what I should be looking for and what kind of commitments I should get to be able to do the job the way Fritz thought it should be done," Biden said at an event honoring Mondale in 2015.

Backstory: Mondale spoke by phone on Sunday with President Biden and former Presidents Jimmy Carter and Bill Clinton, as well as Vice President Harris and Minnesota Gov. Tim Walz, said his friend and former campaign staffer Tom Cosgrove. While he and his family believed his death was imminent, after those calls he “perked up.”

In a final goodbye email to 320 staffers spanning four decades, Mondale told his staffers how much they meant to him, adding he knew that they’d keep up “the good fight” and “Joe in the White House certainly helps.”

The email, which was shared with Axios, was prepared to be sent upon his death.

Cosgrove said Mondale had been deeply worried about the impact of a potential second Donald Trump term on American democracy. "There was a difference after the inauguration - a letting go,” Cosgrove said. “There was a big exhale of relief.”

Mondale and Carter were the longest-living post-presidential team in U.S. history.

In his 1984 presidential run, Mondale nominated New York congresswoman Geraldine Ferraro as his running mate, making her the first female nominee for vice president of any major American party.

He was awarded the Public Leadership in Neurology Award from the American Academy of Neurology in 2015 for raising awareness for brain health, after he lost his wife, Joan, and daughter, Eleanor, to brain diseases.

Mondale served as Minnesota's U.S. senator from 1964-1976. He also served as former President Clinton's ambassador to Japan.