Star Saber

A relic of the Primes of Cybertron, the Star Saber was forged for Prima by Solus Prime. Said to wield the power of the Matrix of Leadership, the Star Saber is capable of cutting through almost anything, and can fire energy waves strong enough to knock a Decepticon warship out of the sky. Kept by the Primes until Zeta Prime's death, Alpha Trion sent the sword to earth during the war for Cybertron, knowing Optimus Prime would eventually find his way there. Though Megatron was the first to try and obtain the blade, it was only released from its containment in a mountain by Optimus, who then used it to send the Decepticons fleeing.
Seeking to match its power, Megatron stole the arm of a deceased prime and grafted it to himself, and used the Forge of Solus Prime to create the Dark Star Saber, a weapon forged from Dark Energon and able to be used by any Decepticon. In a battle in Egypt for the first Omega key, the two most powerful weapons in the universe clashed, and though Optimus fought valiantly, the Star Saber shattered from a final hit from its stronger twin. The broken blade would not see action again until Dreadwing betrayed the Decepticons and gave Optimus the Forge of Solus Prime. After rebuilding the sword and building a Space Bridge, Optimus and Team Prime battled to regain the four Omega keys, only to surrender when their human allies were placed in jeopardy. In order to save them and earth, Optimus sliced Megatron's arm off and destroyed the Omega Lock, dooming Cybertron to remain lifeless.
Upon their return to earth and upon discovering that the Decepticons had discovered the Autobot base, Optimus used the Star Saber to hold off the incoming armada, and then destroy the ground bridge in order to prevent his evacuating comrades from being captured. It was all for naught however when Megatron's crew destroyed the base as the hammer blow fell. Though Optimus was rescued and revived by Smokescreen, the Star Saber was left to become Megatron's trophy, where it remained until Smokescreen and bumblebee retrieved it during the final battle against the remaining Decepticons over earth. As bumblebee tried to even the battle between Optimus and Megatron, the Decepticon commander killed the Autobot scout, and prepared to kill Optimus only for Bumblebee, who fell through a rebuilt Omega Lock and into life-restoring Cybermatter, to use the Star Saber for the final time against Megatron, ramming the mighty weapon through the brutal warlord's chest and killing him once and for all.