Battlestar Galactica
One of the, or maybe the most successful of the Star Wars competitors, conceived as a pilot for a TV series that could be aired as a couple of episodes or shown as a movie in theaters, it went through some revisions until it finally landed, but it did pay off.
The first concepts would have featured a huge, impressive spaceship (the titular "battlestar") leading a fleet of refugees in a desperate search for Earth, fleeing from a crushing defeat at the hands of an alien enemy, the dreaded "Cylons". There would be an "ancient astronauts" subtext with many characters having classical or mythological inspired names and Earth being referred to as a "lost planet" and being occupied by primitive civilizations when found, implying that the characters would be the origin of the gods and heroes of several classical myths.
That storyline ended up being shelved, the massacre and near destruction of the protagonists civilization was thought to be too dark and the writers just couldn't come up with a satisfying way of having the fleet discover a primitive Earth while also defeating the Cylons, a suggestion to use a modern day Earth as also discarded. Finding Earth after all the mystery and anticipation would always be underwhelming, it seemed.
So, the whole thing was rethought, since they were raiding the classics for character names and such, why not look to them for a basic plot, maybe something like the... Odyssey?
And so a new plot was put together, a lot of things carried over from the earlier iterations, humanity being split in 12 nations named after the zodiac, the classic and mythological character names, the Cylons, the starfighters, but the plot took a whole new direction...
Humanity has long fought a terrible war against the Cylons and now victory is within reach as the last enemy space fortress is under siege by a united human fleet. But the Cylons play a last card with the help of a traitor (John Colicos), triggering a super-weapon that destroys the human flagship, thankfully some quick thinking by one of the human captains, Adama (Terry Carter), enables the humans to exploit a vulnerability in the weapon and the fortress is captured, the Cylons are crushed, a huge number of prisoners is freed and the victorious captains meet to discuss the return home...
But there's a problem, the destruction of the Cylon super-weapon caused a "hyperspace disturbance", the human ships will have to take some circuitous, hazardous routes to reach their homes, and the path of Adama's Capricans will have to cross some of the wildest untamed regions.
Still, needs must, and the journey begins, Adama will have to lead his forces and a convoy of freed Caprican prisoners through the many dangers that stand between them and their homes, thankfully he will have the help of two excellent subordinates, "first spear" Apollo (Richard Hatch), and "master of the ship" Nestor (Lorne Green). Also the fleet's first stop will bring Starbuck (Dirk Benedict) on board, a skilled mercenary and scout, free spirit, jokester and gambler. Two action heroes to take care of most of the action scenes, a commander always ready to come up with a stratagem to overcome the problem of the week or to encourage the fleet at a critical moment, and a grey-haired advisor with the bits of wisdom that will lead to a solution whenever things appear hopeless.
Along the way they will run into assorted aliens, dangerous spatial "maelstroms", the "Cyclops" a forgotten (but still active) Cylon super-heavy cannon, and other problems. Also, Baltar the traitor will show up a few times to stir up trouble, leading a ragtag band of Cylon remnants and having turned to piracy and banditry to survive after his escape. Another recurring guest is the mysterious Circe (Anne Lockhart), a scientist at the controls of her own incredibly advanced spaceship, sometimes she will put the Capricans in danger with her experiments, some other times she will help them against a troublesome alien or anomaly.
All of this went into making a successful, if expensive, series (the two pilot episodes where indeed put together and released as a movie, but most people nowadays remember the series), the original series ran for three seasons and was quickly followed by another two spin-off series that reused models, props and actors of the original, one set in the Human-Cylon war, and the other following further adventures of Starbuck. The models in particular became a very familiar sight to viewers as they would find their way into several sci-fi productions, recycled and tweaked in many ways, with the powers that be being determined to get the best mileage out of them.