Complex sentence: Roy Huggins developed "Colt.45" with Wayde Preston in the part of undercover government agent Christopher Colt, who takes the cover of a travelling Old West pistol salesman, hence the double entendre of the title of the series.
Split into simpler sentences: Roy Huggins developed "Colt.45" with Wayde Preston in the part of undercover government agent "Christopher Colt". Colt's cover is that of travelling Old West pistol salesman, hence the double entendre of the title of the series.