Idris Elba is on board for the lead of ”Pacific Rim” with Guillermo del Toro directing the Legendary/Warner Bros.’ sci-fier.The pic, which already stars Charlie Day and ”Sons of Anarchy” star Charlie Hunnan, centers on an alien invasion that threatens earth and the humans who come together to defend it. Project went into development in May 2010 with ”Clash of the Titans” scribe Travis Beacham writing the script. Legendary acquired the rights to Beacham’s project as part of its co-financing and co-production deal with Warner Bros. Legendary topper Thomas Tull is producing along with Jon Jashni. Production is expected to get under way this fall. Legendary had shown strong interest in Elba (”Thor”) to take a role, and at one point Alexander Skarsgard was being pursued. Skarsgard passed because of his ”True Blood” commitments. Elba is repped by UTA.