June Foray - Rocky the Flying Squirrel, Natasha Fatale, others
Bill Scott - Bullwinkle J. Moose, Mr. Peabody, Fearless Leader, others
Paul Frees - Boris Badenov, narrator (Jet Fuel Formula only)
William Conrad - Narrator
Hans Conried - Snidely Whiplash
Walter Teatley - Sherman
The Rocky & Bullwinkle show is arguably Jay Ward's most well-known cartoon, and it's pretty easy to see why. The show follows the adventures of Rocky the Flying Squirrel (an all-American boy in the form of a squirrel), and his extremely dimwitted sidekick Bullwinkle J. Moose, who were constantly spied on by Pottsylvanian spies Boris Badenov and Natasha Fatale. The moose-and-squirrel duo would also be accompanied by a variety of other shorts in their program (my favorite of which is Peabody's Improbable History). The show was the first to be animated by Mexican studio Gamma Productions; initially, the animation (as well as the artstyle) was shockingly cheap, even for 1959 standards - animation errors were rampant and characters would sometimes be off-model. It got to a point where Jay Ward Productions regulary sent animators overseas to supervise the episodes in an effort to prevent future mistakes. Here's some examples of the show's limited animation:
Before the idea of the current show was created though, the characters of Rocky & Bullwinkle themselves were created as part of an unproduced animated series called "The Frostbite Falls Revue"; however, that idea was scrapped and the two characters were given their own show. In fact, Bullwinkle wasn't even known as Bullwinkle until the show was under development - he was originally known as "Canadian Moose" before his name was changed to Bullwinkle. During the development stages, Rocky & Bullwinkle were given archrivals to better balance out the series - Boris Badenov and Natasha Fatale (whos appearances were inspired by both Gomez and Morticia Adams respectively). Boris and Natasha were Pottsylvanian spies who were sent out by Fearless leader to either kill / steal somthing from Rocky and Bullwinkle. Of course, due to them being villains, none of their plans worked and most of the story arcs always ended with Boris telling Natasha to "SHADDAP YOUR MOUTH!".