Jose Jones "J.J." Castillo was the voice actor for Mercury Black in RWBY before he left Rooster Teeth and Yuri Lowenthal took over the role. He also suggested the full name for the character.
J.J. was previously in charge of the RT Recap and various live action projects at Rooster Teeth Productions. He was also the editor of Achievement Hunter's Let's Build series and hosted the weekly film and television podcast, Screen Play.
He left the company in January 2015 in order to pursue other projects. He currently hosts a film and television podcast called Film Geek Army.