The "Star Trek" universe is vast and complicated. Most of the "Star Trek" shows to date take place on Federation vessels or stations staffed by career officers on specific assignments. The franchise largely revolves around managerial professionalism and workplace propriety. There is respect for the chain of command, and orders are given and followed as a matter of course. Starfleet is a military organization, but with its militant strictness devoted to exploration and diplomacy rather than combat and conquest. Ships are assigned to distant areas of space where they are tasked with examining a curious pulsar or, say, to a disease-ridden world in need of medicine. The bureaucracy works in "Star Trek," and individuals go where they are needed.

As such, when a minor character appears on "Star Trek," Trekkies assume that they merely arrived on the U.S.S. Enterprise (or Deep Space Nine, etc.) because they were needed there. An itinerant expert may be called in to complete a specific mission and then, once completed, they will merrily fly off to another. We understand that any character on "Star Trek" could be reassigned at any minute. So, when a minor character vanishes, it's safe to assume they experienced a career shift. Central characters only tend to stick around because a starship captain has assembled a senior staff they prefer ... and also because the actors involved in bringing them to life have signed long-term contracts.

But for those of us who like those supporting characters, a small word of explanation would have been nice. "She was transferred" is all that's really required. Below are five "Star Trek" characters that left a mark on the franchise, only to disappear without notice.

(Side note: Certain characters disappeared from the "Star Trek" franchise -- from Yeoman Rand (Grace Lee Whitney) to Ensign Sonya Gomez (Lycia Naff) -- only to re-emerge many years later. Those characters will be absent from this list.)