The actor’s role is being kept under wraps. Fillion has a long history of working with Gunn: He played the voice of a monstrous inmate in Guardians of the Galaxy, Bill Pardy in Gunn’s 2006 horror comedy Slither, and the Holy Avenger in the filmmaker’s 2010 pic Super.
Fillion stars in ABC’s The Rookie, which starts its second season on Sept. 29. Prior to that, Fillion starred for eight seasons as mystery novelist Richard “Rick” Castle on ABC’s Castle. His credits include a number of series, such as Netflix’s Santa Clarita Diet and A Series of Unfortunate Events. Fillion is renowned for his turn as Captain Malcolm ‘Mal’ Reynolds on Joss Whedon’s cult sci-fi series, Firefly, which also spawned the feature movie Serenity.
The actor is no stranger to DC,