Boussh costume of the sort worn by Princess Leia in Return of the Jedi
A Breen soldier from Star Trek Deep Space 9
Interstellar cross-time transdimensional ethnographers have unraveled an unexpected fact. The Breen, best know for the Romulan saying, "Never turn your back on a Breen" and third-rate villains (in the opinion of some) as allies of the Cadassians and Dominion against the United Federation of Planets in the Dominion War, apparently at one time discovered a secret gateway to "A long time ago, in a galaxy far, far, away."
Available evidence suggests the gateway (or wormhole) interlinking Breen space with the Galactic Empire actually landed Breen troops into this far-removed galaxy in the early days of the Galactic Republic. The community of Breen, unable to locate Hoth (a world reported to be like their own--their helmets contain a refrigeration unit to keep them cold), underwent a number of cultural and physical adaptations allowing them to better survive hotter climates.
Eventual linguistic change transformed "Breen" into "Boussh" (according to Breen linguistics, the relationship between the terms is simple and logical). They gained fame in the galaxy as a race of bounty hunters and mercenaries to the extent that Princess Leia Organa could disguise herself as one and enter the palace of Jabba the Hut without raising any suspicion whatsoever.
Speculation that the Breen are actually the secret masterminds of the entire universe is premature at this time. Evidence available as of this point can neither confirm nor deny such claims...
(A fun suggestion for linking worlds--of course many other imaginary crossovers between story worlds based on physical similarity are possible. For example, between Vulcans and Elves...;)