It's Martin Luther King Jr. Day

 

Martin Luther King Jr. Day is a federal holiday in the United States, observed on the third Monday of January each year, to honor the civil rights leader Martin Luther King Jr. and his contributions to racial equality and social justice. 

 

According to Britannica:

Almost immediately after King’s death, there were calls for a national holiday in his honor. Beginning in 1970, a number of states and cities made his birthday, January 15, a holiday. Although legislation for a federal holiday was introduced in Congress as early as 1968, there was sufficient opposition, on racial and political grounds, to block its passage. In 1983 legislation making the third Monday in January a federal holiday finally was passed, and the first observance nationwide was in 1986. The day is usually celebrated with marches and parades and with speeches by civil rights and political leaders.