Martin Luther King Jr., a reverend and civil-rights activist, was assassinated at 39. However, he inspired several movements and political changes.

The holiday falls on the third Monday of January. A bill to make Martin Luther King Jr. Day a federal holiday was introduced on April 8, 1968 — four days after King was assassinated, according to the National Museum of African American History and Culture.

It was first proposed four days after King’s 1968 assassination outside a Memphis motel. It took 15 years until it became a federal holiday.