Star Saber

The Star Saber is one of the most powerful ancient Cybertronian weapons, and is said to hold the power of the Matrix itself. It was designed and built by Solus Prime using her Forge. Its immense power is so great, that it can slice a huge boulder in two and fire energy waves at long-range targets. This relic can only respond to the power of a Prime alone. Even without a Prime to wield it's power, the Star Saber could be used like a real sword.

Creation
The Star Saber was created by Solus Prime with her Forge back on Cybertron. It holds the power of the Matrix, but it can only be wield by the hand of a Prime. During the battle against Unicron, Prima, the first ever Transformer, wielded it in battle.

Exlie
The Star Saber was among the powerful relics that Alpha Trion sent to Earth for Optimus Prime to retrieve.

Discovery
Megatron had found the locator beacon for the Star Saber, and had sent Soundwave with a fake locator beacon to distract the Autobots. Upon excavating for the relic, Megatron realized that it was the powerful Star Saber and attempted to pull it out, but it was stuck inside a boulder. He tried to blast it out, but the boulder was unscatched, revealing that the sword created a shield surrounding. He then ordered his tropps to move the boulder so that Optimus could never obtain it.

Smokescreen had followed the beacon with Jack Darby, and instantly recognized the relic. Jack contacted Ratchet so he could send back-up. The rest of the Autobots arrived, and Optimus reached the Star Saber's handle and pulled it out.

Megatron, enraged, sent the huge boulder down the mountain in an attempt to squash him. However, the sword's power was so great that it cut the boulder cleanly in half. He then sent a huge energy wave that rocked The Nemesis for a while (plus damaging it).

Alpha Trion's Message
Back at the Autobot Base, Optimus Prime received a message from Alpha Trion explaining that he sent the relics to Earth as he had a vision that the Autobots would visit that planet, and, now that he has the Star Saber, he would allow the last four relics, the Omega Keys, to be found.

Meeting its Counterpart
After Arcee and Smokescreen failed to recover the first Omega Key, Optimus went to duel Megatron for it. He discovered that Megatron had created his own Dark Star Saber, built from Dark Energon using the Forge of Solus Prime. After a lengthy duel, Megatron had the upper hand and destroyed the Star Saber, reducing it to its hilt.

Optimus and Smokescreen escaped with the Omega Key, but left Megatron happy, as he knew he now had a great advantage over the Autobots.

Reforging
Optimus managed to bring back the Forge of Solus Prime with the help of Dreadwing and reforges the Star Saber. He then took it to battle Vehicons and later Megatron in a lengthy duel on Cybertron for control over the Omega Lock. Optimus Prime gains an advantage when he hits Megatron with a blue energy wave, knocking him off his feet. The Autobots then succeed in controlling the Omega Lock.

Battle of the Omega Lock
Optimus used the Saber to fight the Decepticons and later used it to cut off Megatron's sword hand and destroy the Omega Lock.

Defending the Base
Optimus used the Saber to fend off Decepticons attacking the Autobot Base and later used it to destroy the Space Bridge controls. The blade survived the base's destruction, intact, and was stored aboard the Nemesis.

Battle for Earth and Cybertron
Though Smokescreen did not retrieve it or make mention of it he noticed the Star Saber was in the vault of the Nemesis. When the Autobots invaded the ship, Smokescreen was the last to board. As the others went he saw Megatron with the Dark Star Saber. Shocked by its survival, Smokescreen desperately ran to get the Star Saber for Optimus. Arcee was ticked when he would not say what he was going to get. With the sword he ran to the Omega Lock 2.0's control station. He saw Optimus and Megatron fighting below and prepared to launch the sword below. Shockwave then shot him causing him to drop the sword. Both sides scrambled for the sword, with Bumblebee securing it. Ratchet told Optimus to destroy the Omega Lock with the Star Saber. However, Megatron killed Bumblebee but not before he knocked Optimus out of Bumblebee's line of sight to prevent Optimus from getting a hold of the Star Saber and destroying the Omega Lock again. The scout fell into a pool of Cyber Matter with the Star Saber next to him. The Cyber Matter resurrected Bumblebee, with voice box included, and he used the Star Saber to stab Megatron's spark, avenging himself, countless others and saving the life of Optimus Prime. The Star Saber has since returned to the Last Prime.

Predacons Rising
Optimus Prime used the Star Saber to promote Bumblebee from "Scout" to "Warrior".

After that, it was never seen again. With the loss of all the lineage of the Primes, the Star Saber is now an ordinary, big sword. (Unless Alpha Trion is still out there or if Optimus will return again).