Kagato

Kagato is a being of immense intelligence and power. He wanders the universe collecting artifacts from civilizations and stealing them from museums, often destroying them in the process. He keeps them on his ship, which also serves as a mobile command base and power control system, preventing his energies from being drained in prolonged bouts. It also sports a full-sized orchestral organ in the main chamber. His intelligence and cunning are enough that he even managed to capture Washu, whom he once worked with.
He came to Earth in OAV episode five, having tracked Ryoko down to recapture her and force her to do his bidding again. During the encounter he fought against Tenchi, winning easily, and then against Yosho who wielded the sword Tenchi against him but was unable to prevail. The battle a draw, Kagato retreated to his ship with Ryoko, placing her inside a containment field.
Though Ayeka and the others gave chase to his ship, with Ryo-Ohki carrying Ryu-Oh's control module with Tenchi inside operating the Lighthawk wings, Kagato proved too strong with his ship. The beam destroyed the shield that had been formed from Ryu-Oh's lighthawk wings and destroyed Tenchi.
Later on, a revived and rejuvenated Tenchi once again faced off against Kagato, and this time Tenchi prevailed, cutting through both Kagato and his ship. Kagato evaporated and his ship exploded while they escaped.