The character originally appeared in Robert E. Howard's story Delcardes' Cat, and is getting his own comic book series (courtesy of Dynamite) next year.
You probably remember Thulsa Doom as being played by the incomparable James Earl Jones in the classic Conan the Barbarian movie. But if you're a fan of Howard's work, you know that Jones' character didn't resemble the literary one very much. The original Thulsa Doom is an undead sorcerer with the face of a skull, with eyes of fire, and all kinds of scary powers.
So, unless Hounsou is going to bury his handsome face behind make-up or CGI, the new Thulsa Doom will be more in line with Jones' character, and another departure from Howard's original pulp stories. Already, they are looking to make a demonic villain more inviting, as Hounsou's film will show how the once heroic Doom went all mean and nasty. Just once, wouldn't it cool to have a movie about a demonic sorcerer who happily eschewed the straight and narrow? Thank goodness J.R.R. Tolkien left no such wiggle room with Sauron or Morgoth, eh?