Sextus is one of the many Spartan Guards (Platinum series) than operate in Khera. Programed with a blind loyalty to his masters, Leo is the personal Spartan Guard from Lord Herm. He served as bodyguard for Lord Emp during a open Kheran senate meeting, but he was unaware about the danger than that event implied.
Same as all the other Spartan Guards, Sextus have the same facial features than Spartan.