Star Trek: 12 Subplots That Went Nowhere

While Thomas Riker could've been relegated to a single appearance in Star Trek: The Next Generation's "Second Chances" and still been one of TNG's most intriguing "guest" characters, the producers rightly saw that he was a good fit for Star Trek: Deep Space Nine's rougher around the edges tone and brought the Riker double back for "Defiant".

"Defiant" continued Tom's arc established in TNG, showing him chafing against his role as a the "second" Riker and hooking up with a band of Maquis for a suicide mission to destroy a secret Obsidian Order fleet. The episode concluded with Tom hauled off to Cardassian prison but with a kiss and a promise from Major Kira that they would meet again.

And then they never did... and Thomas Riker presumably spent the rest of DS9 in a Cardassian labor camp (or worse), not withstanding his frequent reappearances in non-canon Star Trek lit.

It's still not clear why DS9 chose not to follow up on its own explicit promise to rescue the character, but Thomas Riker was included in internal materials from the producers as a topic the writers were absolutely not interested in revisiting. Apparently the Star Trek Universe just wasn't ready for two Rikers.