According to TFwiki, The Guardian of "forces so grand that entire galaxies could be devastated with them" is an immortal creature of much power and much mystery. The weaponry he protects was produced long ago by a race that was around at the beginning of the universe, but whether he is of that race, one of their creations or in charge of their legacy through some other connection is untold.
Its eyes shoot beams that can destroy a cybertronian.
The Guardian, as its name says, is the guardian of a spaceship created by an ancient race. This spaceship has technology that can level planets and erradicate galaxies.
The Guardian can take shots from Autobots's weapons. Optimus Prime decides to retreat and leave the creature after seeing its power and durability.