* He first envisioned the entire saga as a six-part story. He then wrote Episode IV: A New Hope (released in 1977) as the first installment. This was the only script he initially completed.
* He then wrote the script for Episode V: The Empire Strikes Back (released in 1980), which was the second film to be released, but chronologically the third in the story.
* Episode VI: Return of the Jedi (released in 1983) was written last, becoming the final installment chronologically and the third to be released.
* Later, Lucas revisited the story to create Episodes I, II, and III, which form the prequel trilogy. These were written and released between 1999 and 2005, after the original trilogy had been completed.
Therefore, the order he actually wrote the movies in is:
1. Episode IV: A New Hope
2. Episode V: The Empire Strikes Back
3. Episode VI: Return of the Jedi
4. Episode I: Phantom Menace
5. Episode II: Attack of the Clones
6. Episode III: Revenge of the Sith
It's important to note that he conceived the entire story as a six-part saga before writing any of it.