While no details about the villain have been revealed, there are rumors that the Klingons could emerge as an evil force, since they have not been fully shown in the first two movies. That has yet to be confirmed. Paramount and Skydance Pictures would not comment on the casting, or the villain's identity. Even if Idris Elba's character is a Klingon, we likely won't know until the sequel hits theaters. You may recall that it was long assumed that Benedict Cumberbatch's "John Harrison" was actually Khan in Star Trek Into Darkness, but no one would confirm that until the movie came out in May 2013.
Justin Lin is directing from a script by Simon Pegg and Doug Jung, with Star Trek and Star Trek Into Darkness director J.J. Abrams producing alongside Bryan Burk and Skydance's David Ellison. Idris Elba most recently starred in The Gunman, and he will next be seen in Avengers: Age of Ultron as his Thor character Heimdall, and The Jungle Book. He also recently wrapped on Bastille Day and he is also lending his voice to the Pixar sequel Finding Dory.
Star Trek 3 comes to theaters in 2016 and stars Chris Pine, Zachary Quinto, Simon Pegg, Karl Urban, Zoe Saldana, Anton Yelchin, Idris Elba. The film is directed by Justin Lin.