Ne-Yo revealed to Britain's Sunday Mirror that he had to turn down the role of Martin Luther King because it would require him to gain 30 pounds! 

Ne-Yo said "The want to start shooting at the time my album R.E.D. comes out, and wanted me to gain 30 pounds, so i couldn't do it," Ne-Yo admitted "I'm kicking myself but acting can't take the place of my music."

http://allhiphop.com/2012/07/24/non-hip-hop-rumors-which-singer-turned-down-the-chance-to-play-martin-luther-king/