May 25, 1977
Season 6 premiered on the Netflix streaming service on March 2014.
Hundreds upon hundreds of actors, from the well known to uncredited extras have acted in the Star Wars films over the 40 years since A New Hope premiered.
Stars Wars: A New Hope debuted on May 25, 1977.
It's already premiered
As of 10/3/11, Season 4 of Star Wars: The Clone Wars premiered 3 weeks ago.
Premiered May 5, 1977 in the USA
It was Star Wars Episode IV/4 A New Hope, which came out in 1977.
If you mean when Star Wars: The Cone Wars first aired, after the pilot film was no longer playing in theaters, Season 1 premiered on October 3, 2008
Yoda did not appear in the original Star Wars, A New Hope.
Star Wars IV: a New Hope comes before Star Wars VI: Return of the Jedi.
If you mean when the TV series Star Wars: The Clone Wars first aired, it was on October 3, 2008 (The pilot film for the series premiered in theaters on August 15, 2008)
Star Wars IV - A New Hope