MLK Day has been designated as a national day of service (Credit: National Park Service/ CC BY 2.0/ Wikimedia Commons)

Martin Luther King, Jr. (MLK) was one of America's most influential civil rights movement leaders. His life and achievements are celebrated annually on the third Monday of January. The federal holiday, which will be observed on January 16 this year, is designated as a National Day of Service. Americans are encouraged to spend the holiday volunteering to improve their communities.