In the U.S., Martin Luther King, Jr. Day is celebrated on the third Monday in January, which is the 21st this year.
King was the chief spokesman for nonviolent activism in the civil rights movement, which successfully protested racial discrimination in federal and state law. The campaign for a federal holiday in King’s honor began soon after his assassination in 1968. Ronald Reagan signed the holiday into law in 1983, and it was first observed on January 20, 1986. At first, some states resisted observing the holiday as such, giving it alternative names or combining it with other holidays. It was officially observed in all 50 states for the first time in 2000. (Wikipedia)
Some states observe MLK Day as a day of service, taking the opportunity for charitable and humanitarian action.