Return of THE Jedi, not a Jedi.

For words where the plural and singular are the same, you should use 'the' to refer to the group, and 'a' to refer to the singlar.

"The migration of the salmon" refers to all the Salmon migrating, not one.

It's the Return of the Jedi as an orginisation,

Return of the Jedi, not a Jedi.

For words where the plural and singular are the same, you should use "the" to refer to the group, and "a" to refer to the singular.

"The migration of the salmon" refers to all the Salmon migrating, not one.

It's the Return of the Jedi, as an organization.