The Negh'Var class long-range torpedo ship (okay, it's not, but I've played enough Birth of the Federation that it's what I think of it as) is the largest Klingon ship (to date) ever shown on film. And by film, of course, I mean TV. It has never appeared in any of the films.
But what it does have is the interesting distinction, not well-published, of appearing in every Star Trek series finale.
The ship model was created for the final TNG episode "All Good Things..." where it famously curdled the USS Pasteur as the two Captain Picards searched the Devron system for an anti-time eruption that they actually caused even though it's supposedly all three Enterprises that generated it.
They got their commuppance however: it turns out the Klingons are no match for a super-powerful USS Enterprise with a giant laser cannon of death.
That much money spent on models can't just be wasted, however, and when the Klingons made waves on Star Trek: Deep Space Nine it was time to dust off the old prop and throw it on screen as the new Klingon flagship, the I.K.S. Negh'Var. Once the Dominion War was in full swing, the Klingons had a raft of them (the mirror universe Klingon-Bajoran-Cardassian Alliance had a giant one that it's best that we stop talking about because the later mirror universe episodes stunk to high heaven), and therefore when the Alpha Quadrant's forces leave Deep Space Nine for the final confrontation on Cardassia Prime in the clunkily named "That Which You Leave Behind", of course you'll see the Negh'Var four times at once. A barrel of bloodwine to the first man who steps over the rotting corpses of dead Cardassians!
A couple years later is was time for Star Trek: Voyager's final episode, the infamously bad "Endgame". In an alternate-universe "All Good Things" a super-powered Enterprise took care of two Negh'Var in the year 2395. "Endgame" takes place in an alternate-universe nine years later in 2404, and now somehow two massive Negh'Var warships are no match for an old woman, a shuttlecraft, and a ship inexplicably captain'd by Harry Kim.
It has nothing to do with the Negh'Var mind you, but did you notice (as I didn't during my review) that at the end of Endgame there is an Excelsior, Galaxy, and Defiant class ship reflecting the previous TV series (or the movies, in the Excelsior case). It's a nice little nod-back, even though obviously the Enterprise-D has long since been replaced by the Enterprise-E, and it would at best be the re-renamed USS Defiant since the original was destroyed by the Breen, and Sisko is currently floating in some wormhole-alien aether right now. Still, nice touch.
So three series finales, three appearances of the same awesome Klingon warship. "But wait!" I can hear you exclaim, "what about the other series finales"? Well, you may not know it, but the Negh'Var makes an appearance in those as well.
Everybody remembers that Riker and the Enterprise-D appears in "These Are the Voyages..." (First TV Drama called the episode "Trip dies in Riker's holodeck"), but did you notice the Klingon warship they snuck into one of Connor Trinneer's big acting scenes?
But this is nothing new. Hell, they've been putting the I.K.S. Negh'Var in TV finale episodes since 1969.