On the third Monday of January every year, the federal government closes up shop for a day to honor civil rights hero Martin Luther King, Jr. - who was assassinated in Memphis on April 4, 1968.

But the road to Martin Luther King, Jr. Day was fraught. It didn't become a federal holiday until 1986, nearly 20 years after it was introduced to Congress, per the King Center. Even then, it faced an upward battle for all states to recognize the holiday, only getting nationally recognized in 2000.

While the nation recognizes King as an "icon for democracy" today, in the 1960s and 1970s, he was still a controversial figure, according to Michael Honey, an American historian and professor of humanities at University of Washington, Tacoma.

"This was the first holiday around a national figure who is not a president, and who is African American," Honey said. "Many in Congress did not want to recognize an African American that was thought of as a troublemaker by some in his day."

How did Martin Luther King Jr. Day come to be a federal holiday?

On April 8, 1968, Rep. John Conyers, D-Mich., introduced legislation for a federal holiday, according to The King Center.

The next year, on Jan. 15, 1969, annual ceremonies commemorating King's birthday were launched by The King Center in Atlanta. It called for nationwide ceremonies and began working to gain support for the holiday.

In the 1970s, support for a national Martin Luther King Jr. holiday grew. Several states, including Illinois, Massachusetts and Connecticut, become the first states to enact statewide King holidays, but Congress failed to act on a national level, according to The King Center.

In 1979, President Jimmy Carter called on Congress to vote on the King Holiday Bill. Not everyone was on board, and the bill was defeated by five votes in the House in November 1979.

Despite years of setbacks, King's widow, Coretta Scott King, continued to fight for approval of the holiday and testified before Congress multiple times.

How does Stevie Wonder factor into the history of MLK Day?

Following the defeat of the bill, Stevie Wonder released "Happy Birthday," in support of enacting a national Martin Luther King Jr. holiday, according to The King Center.

The song became a hit, and in the early 1980s, Wonder worked with Coretta Scott King to gain support for the national holiday, according to the King Center.

Coretta Scott King fought for years to get the holiday to honor her husband

In 1982, King and Wonder delivered a petition with 6 million signatures in favor of the holiday to the speaker of the House.

On Nov. 3, 1983, President Ronald Reagan signed a bill marking the third Monday of January, as Martin Luther King Jr. Day, according to the center. The holiday was to begin in 1986.

In January 1986, the first national Martin Luther King Jr. holiday was observed. According to the center, by this time, 17 states had already enacted King holidays.