The phrase ‘That’s all, Folks!’ was first used at the end of a Looney Tunes cartoon back in 1930. It was spoken by the character Bosko. In 1929, another Bosko cartoon had a line ‘So long, folks!’ so it has changed once. This phrase may have been influenced by a 1926 British Cartoon which ended with ‘And That’s All!’.
A lot of other characters have used the phrase since then. The stuttered version ‘Th-th-th-that’s all folks!’ by Porky Pig is probably the best remembered version of the line.
The voice behind many of the Looney Tunes characters, including Porky Pig, was Mel Blanc. Even today, he is recognised as the father of voice acting. His grave marker includes what has become one of the best-known of all epitaphs – ‘That’s All Folks’