Former U.S. Rep. John Conyers, a civil rights icon who during five decades in Congress co-founded the Congressional Black Caucus and pushed to establish a national holiday to honor the Rev. Martin Luther King Jr., died Sunday of natural causes at the age of 90.

His death comes after a long and illustrious career that spanned more than 50 years and 27 terms in office, but ended in 2017with a sudden resignation amid claims of sexual harassment and verbal abuse of employees and misuse of taxpayer funds to cover up those claims.

Conyers' tenure was a remarkable 53-year-run during which the lawmaker, the son of a well-known labor lawyer in Detroit, compiled a near-record legacy of civil rights activism, longevity and advocacy for the poor and underprivileged.

He died with the sixth-longest tenure in congressional history.

"For a long time he was black America's congressman," said Sam Riddle, a longtime family friend and consultant to the Conyers family, who confirmed the death Sunday. "On the streets of Detroit, he'll be mourned."

Detroit Mayor Mike Duggan in a statement said he "was deeply saddened" by Conyers' death.

"One of my most special memories was spending time with him at Gordon Park on 12th Street and Clairmount on the 50th anniversary of the violence of 1967 as he recounted the story of his courageous efforts to calm the angry crowds," Duggan said. "He has fought for a better Detroit for more than half a century.

"From co-founding the Congressional Black Caucus to leading the fight in Congress to enshrine Martin Luther King’s birthday as a national holiday, John Conyers’ impact on our city and nation will never be forgotten," Duggan said.

Michigan Gov. Gretchen Whitmer called Conyers a "lifelong Detroiter who was deeply committed to the city and to those he represented."

"His impact on our state, whether by spearheading reforms in criminal justice and voting rights in Congress or through his lifetime of civil rights activism, will not be forgotten," Whitmer said in a statement.

Conyers was born in Detroit and graduated from Northwestern High School. After a tour of duty with the U.S. Army during the Korean War, Conyers returned home to earn bachelor's and law degrees from Wayne State University.

His law practice and work in the auto plants in Detroit led him to the office of former U.S. Rep. John Dingell, D-Dearborn, where he worked as a legislative assistant for three years. But by 1964, at the age of 35, Conyers went after a seat of his own in Congress, winning the first of 27 general elections and serving portions of Detroit and some surrounding Wayne County suburbs for the next five decades.

U.S. Rep. Debbie Dingell, D-Dearborn, recalled Conyers' work with her husband.

“They both believed in justice and equality for all. John Conyers spent his life championing those causes," she said. "The fights John Conyers fought will be remembered for generations."

Conyers may not have had many bills that carried his name — only 26 of the 712 bills he introduced became law, according to the Library of Congress — but he fought for issues of civil rights and social justice, including seeking reparations for the descendants of African-American slaves, modifying the mandatory sentences for those convicted of non-violent drug crimes, defending assaults on the Voting Rights Act, reforming laws that put juvenile offenders in prison for life and calling for investigations into police brutality of African-American men.

And he was the key sponsor of the bill, introduced each session for 20 years, that designated the third Monday of January as a federal holiday in honor of Martin Luther King Jr. Conyers introduced the bill four days after King was assassinated in 1968, but it wasn’t signed into law until 1989.

In the thick of the civil rights battles, Conyers walked alongside King and other leaders of the movement in Selma, Ala., to bring equal voting rights to blacks.

In 2015, during his 50th year in Congress, Conyers told the Washington Post that King was one of the most important historical figures in history.

"I felt the civil rights movement was a powerful chapter in American history, King to me is the outstanding international leader of the 20th century without every holding office," he said. "He advanced us forward even though there was a terrible loss of life and violence and injustice. But Martin Luther King Jr. moved us in a way that changed history."

He moved among those involved in the disturbance in Detroit in August 1967, urging calm. And he burnished his civil rights record even more by hiring icon Rosa Parks after she moved from Alabama to Detroit. The secretary and receptionist job in Conyers' Detroit office was a job she held until her retirement in 1988.

Tributes pour in

U.S. Rep. Rashida Tlaib, a Democrat who won election to Conyers' seat after his resignation, on Twitter called Conyers "our Congressman forever."

"He never once wavered in fighting for jobs, justice and peace," Tlaib tweeted. "We always knew where he stood on issues of equality and civil rights in the fight for the people. Thank you Congressman Conyers for fighting for us for over 50 years."

U.S. Rep. Brenda Lawrence, D-Southfield, also took to Twitter to mourn Conyers' passing:

"John Conyers spent a lifetime in public service dedicated to civil rights and justice for people of color in America. His legacy will continue to impact generations to come."

Republican Congressman Fred Upton of St. Joseph also praised Conyers, calling him "a legend on the House Judiciary Committee" who witnessed and helped write history.

"His positive work on Civil Rights legislation began to move the country in the right direction and made our nation a better place today," Upton tweeted.

U.S. Senate Gary Peters, D-Michigan, said that while serving in Congress with Conyers, he saw firsthand his dedication and passion.

“From being in Selma, Alabama, on Freedom Day during the Civil Rights Movement — to co-founding the Congressional Black Caucus, chairing the House Judiciary Committee and becoming Dean of the House of Representatives — Congressman Conyers dedicated his life to fighting for civil rights," Peters said.

Michigan Congressman Dan Kildee noted that Conyers rose to become the longest serving African American in Congress and dean of the U.S. House of Representatives.

"Throughout his life, John Conyers helped to advance many important causes, including expanding voting rights and equal rights for all Americans," Kildee said.

Mary Barra, chairman and CEO of General Motors, in a statement said Michigan and the country "have lost a true servant of the people.”

“John Conyers was a powerful advocate for equal rights and he was a distinguished member of Congress for more than 50 years," Barra said.

Wayne County Prosecutor Kym Worthy called Conyers "a true Detroit icon and consummate civil servant."

“He never hesitated or ignored calls for help, solicitations for advice, or pleas for resources over the years," Worthy said in a statement. "I will always remember him for how he lived, worked, helped, and preserved.”

Kary Moss, executive director of the ACLU of Michigan, said Conyers was indispensable to the city on Sept 11, 2001, helping to prevent backlash against our Muslim community.

"RIP," Moss tweeted. "He was of Detroit and for Detroit."

Career ends amid a sex scandal

In the end, Conyers would fall to the #MeToo movement. It was a scandal that was a swift and crushing fall from grace.

Facing a rising chorus of voices demanding he step down because of the sexual harassment claims, Conyers, D-Detroit, refused to do so for several months in 2017.

Conyers resigned in early December 2017 after an article on BuzzFeed.com detailed a secret settlement of more than $27,000 with a former staffer who accused him of making sexual advances toward her and paying her out of funds from his taxpayer-supported office.

Within days, several other women had come forward with accusations against Conyers, who, despite his express denials that he harassed anyone, saw House leaders and members of his own party abandon him, with three of the four Democrats in the Michigan delegation calling for him to resign.

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In addition to Marion Brown, the staffer who received the settlement, six other women claimed they either experienced or saw him touching and rubbing women in his office, making sexual advances toward them or making inappropriate remarks. One of them filed a lawsuit against him early this year and then withdrew it, saying she didn't want to hurt Conyers' reputation.

Another woman, Washington lawyer Melanie Sloan, also told the Free Press that Conyers had verbally mistreated her, forced her to babysit his children and, on one occasion, showed up at a meeting with her at his office in his underwear —though she didn't consider it sexual harassment.

From accusation to resignation, Conyers' colleagues went from being warily supportive, urging caution while an investigation by the House Ethics Committee was completed to issuing outright calls for his resignation, even from at least one fellow member of the Congressional Black Caucus, which he helped to create in 1971.

U.S. Rep. Jim Clyburn of South Carolina, who is the third-ranking Democrat in the House and had been a colleague of Conyers' on the Congressional Black Caucus since 1993, called for him to resign shortly after similar calls by House Speaker Paul Ryan and Democratic Leader Nancy Pelosi.

Conyers' lawyer, Arnold Reed, of Southfield, had reiterated on several occasions that the congressman was not ready to resign and wanted to see the ethics investigation completed.

But with allegations swirling not only over the harassment claims but his use of taxpayer funds to pay at least one settlement, he abruptly stepped down as the ranking Democrat on the House Judiciary Committee, a position he had held for more than two decades.

Then — with media reports that some members of the caucus were privately urging him to resign — he suddenly quit Washington, missing several votes, including one mandating sexual harassment training for members, as he headed back to Detroit and his family.

Conyers record in Congress

During his time in office, which he won with huge margins ever two years like clockwork, Conyers was considered one of the most liberal members of Congress, with a 100% rating from the American Civil Liberties Union, Planned Parenthood and the Human Rights Campaign.

The conservative Freedom Works gave him a 15% rating, while the Club for Growth and Americans for Prosperity give him ratings of 8% and 6% respectively.

Conyers, however, had already come under scrutiny twice from the House Ethics Committee in Congress for possible transgressions in his office.

In 2017, the committee confirmed it was continuing to look at whether he had wrongly paid his former chief of staff more than $50,000 for time she didn't work. Conyers said he was only paying her for accrued leave time and severance as part of a separation agreement reached after she pleaded guilty to a misdemeanor charge of receiving stolen property unrelated to her job.

In 2003, the Free Press reported on complaints from six unnamed Conyers aides who said they were forced to work on various campaigns, including a failed legislative campaign for Conyers' wife, Monica, on government time. A follow-up Ethics Committee report, however, focused on allegations that the congressman used staff to babysit his sons, help his wife with her law studies and chauffeur him to private events.

Conyers' office denied the accusations and eventually reached a deal to ensure staff knew where their responsibilities began and ended. Monica Conyers was sentenced to three years in federal prison in 2010 for taking bribes while she was a Detroit City councilwoman. Her husband continued his high-profile political job amid her legal battles.

In 2014, John Conyers nearly didn’t get the chance to run for reelection because of irregularities in the petitions he filed to run for office. Wayne County Clerk Cathy Garrett said he had used ineligible people to gather signatures, but a federal court disagreed and the Legislature passed a law that people who collected signatures didn’t need to be registered voters.

Free Press Washington Bureau reporter Todd Spangler contributed to this report.

Contact Kathleen Gray: kgray99@freepress.com or on Twitter @michpoligal

An earlier version of this story misstated the year Conyers resigned. He resigned in 2017.