The name of MLK's father was Martin Luther King, Sr. - see:

http://www.stanford.edu/group/King/about_king/

Regards,
Ryan Shepard

(The Nobel Prize website confirms that MLK was born Michael Luther King and that he had his name changed to Martin later. The Gale Group also has a biography that mentions both that MLK's original name was Michael and that his father was Martin Luther King senior. -- KK)