Retro Studios has recently hired Kyle Hefley, the artist behind the Halo series Spartan designs, as lead character artist. Kyle has spent nine years with 343 Industries and has done various Spartan and alien designs and modelling for Halo 4, Halo 5 and the upcoming Halo Infinite. This comes after a recent wave of job listings at Retro Studios, which still has roles like art director and graphics engineer left open.
Kyle Hefley has also done work for games such as Call of Duty: Black Ops and Sleeping Dogs. His experience with the Halo series will no doubt aid his position at Retro Studios, as the sci-fi nature of his artwork will be very beneficial to the development of Metroid Prime 4. You can view his portfolio at his Artstation page.