Originally, Martin Luther King, Jr. was the only non-Episcopalian to have a day on our calendar of feast days. The reasons for his inclusion are, I think, obvious to any student of post-modern American history. [In recent years, however, the Episcopal Church has gone wild and is assigning feast days to anyone who appeals to aesthetic and intellectual tastes of the denominational leadership. Ah, well, plus ça change....]
However, the Episcopal Church remembers him not in January, which is the government holiday, but on April 4th, which was the day of his assassination. It is ancient tradition that martyrs be remembered on the date of their martyrdom.
In anticipation of his feast day, and in recognition of the federal holiday [when the government honors a highly educated American by closing all public schools!], the Episcopal Church readings for Martin Luther King, Jr.'s day may be found here.
And since the media conveniently forget that he was a practicing Christian and person of faith, rather than a "person of government", we remember him by his title "The Rev. Dr.".