According to Digital Spy, Penn Jillette is set to guest star on an upcoming episode of the Defenders. The article states:
He is expected to play a magic shop owner called Reuben Charles who meets the Defenders when they take on a case involving a famous Las Vegas illusionist.
Our friends at iTricks have also received word that Justin Kredible has been chosen to play the role of the "Famous Las Vegas Illusionist." Congrats to Mr. Kredible as well!