Led by the most powerful humanoid in the Galaxy, the Shi'ar Imperial Guard is one team you don't want to mess with. The Imperial Guard is an "elite corps" that has sworn complete loyalty to the ruler of the empire. They helped the mad Emperor D' Ken in his plot to harness the power of the M' Krann Crystal (unknown to them the process would destroy the universe) by battling the X-Men and trying to kill D' Ken's rebellious and good sister, Lilandra. But when she took power, they switch their loyalty to her. The original team were homages to the Legion of Super Heroes. Gladiator (the leader) could fly at super speed, lift over 100 tons, virtually invincible (but some forms of radiation weaken him), has "laser-vision" and doesn't need to breathe for long periods of time. He was based on Mon-El. The other members were phasing Astra (Phantom Girl), the electricity controlling Electron (Cosmic Boy), the super-sensed Fang (Timber Wolf), the shape-shifting Hobgoblin a.k.a Shape-Shifter (Chameleon Boy), the energy-firing Impulse (Wildfire), sorceress Magic a.k.a Magique (Projectra), the super smart Mentor (Brainiac 5), the shrinking Midget a.k.a Scintilla (Shrinking Violet), darkness-controlling Nightside (Shadow Lass), the telepathic Oracle a.k.a. Sibyl (Saturn Girl), the super strong Quasar a.k.a. Neutron (Star Boy), the super strong Smasher (Ultra Boy), the energy-bolt-firing Starbolt (Sun Boy), the electric-bolt-generating Tempest a.k.a. Flashfire (Lightning Lad) and the super-growing Titan (Colossal Boy). Later, non-homage members Manta (create light), Earthquake ("psionically creates Earthquakes"), Warstar (super strong) and Hussar (has a "Neuro whip") joined.
References:
http://upload.wikimedia.org/wikipedia/en/f/f1/Imperialguardwiki.jpgX-Men Ultimate Guide