Complex sentence: Sandburg left the show in 1969, by which time Roy Brown had joined the show as Cooky the Cook; frequent guest magician Marshall Brodien also began appearing as a wizard character which by the early 1970s evolved into Wizzo, the world's wackiest wizard.
Split into simpler sentences: Sandburg left the show in 1969, by which time Roy Brown had joined the show as Cooky the Cook. Frequent guest magician Marshall Brodien also began appearing as a wizard character, which by the early 1970s evolved into Wizzo, the world's wackiest wizard.