Elyes Cherif Gabel (born 8 May 1983) is an English actor. Among his most notable roles, he has portrayed Dr. Gupreet "Guppy" Sandhu in the BBC medical drama Casualty, Dothraki Rakharo in Seasons 1 and 2 of the HBO series Game of Thrones, and P.E. teacher Rob Cleaver in the BBC drama Waterloo Road. He appeared in the ITV drama Identity and portrayed Detective Adam Lucas in Season 3 of Body of Proof. He is currently starring in the CBS series Scorpion as computer genius Walter O'Brien.