Narada

The Narada is a Romulan Mining Ship from the future, crewed by a crazed gang of lunatics. Its massive array of weaponry and distinctly greenish aura makes many people think that the ship itself was actually adapted from Borg technology, or stolen from the Borg themselves. The ship went back in time and destroyed the USS Kelvin for no particular reason, probably to kill Spock. Even though Spock wasn't even on the ship. Because he hadn't even been born yet.

Realising their mistake, the crew began writing formal letters of apology to Starfleet, but they posted it via second class and after 25 years the letters hadn't arrived yet. Kirk decided to take the Enterprise over to the Narada and blow it up, but the Narada made a mad dash for Earth (suprise suprise) and began drilling into the planet for no reason. The Enterprise arrived and activated the Narada's time-travel technology which (for some reason) opened a black hole inside the ship, so the Enterprise blasted the ship into oblivion and it was sent crashing into the black hole.

The ship was destroyed but not all of the crew died. They went on to use the pieces of the Narada to build a smaller ship so that they could finally deliver their letters of formal apology to Starfleet, however their mission will apparently take over 5,000 years to complete.