Complex sentence: He is best known for his role as Duke in the "Rocky" series, and he will reprise this role in the 6th "Rocky" film "Rocky Balboa", which is slated for a December 2006 release.
Split into simpler sentences: He is best known for his role as Duke in the "Rocky" series. He will return as Duke in the 6th "Rocky" film "Rocky Balboa" which is slated for a December 2006 release.