Complex sentence: Leader and founder of G.A.S.P. (Gathering of Awesome Super Pals) Reggie Grabinsky is a fun-loving, silly guy with a loose grasp on reality who can be something that might be considered mature when he needs to.
Split into simpler sentences: Leader and founder of G.A.S.P. (Gathering of Awesome Super Pals) Reggie Grabinsky is a fun-loving, silly guy with a loose grasp on reality. However he can be something that might be considered mature when he needs to.