The Imperial Guard is a legion of super-powered champions from throughout the intergalactic Shi'ar Empire who act as enforcers of Imperial law. An elite corps of the Guard, dubbed Superguardians, protects the ruling emperor (majestor) or empress (majestrix) and carries out their personal directives. The other divisions, the Borderers, aid the governors of conquered worlds in enforcing Shi'ar law.
When the X-Men sought to rescue the Princess-Majestrix Lilandra from her insane brother, then-Majestor D'Ken, they fought members of the Guard. The X-Men and the Guard subsequently clashed again after Lilandra had assumed the Shi'ar throne and sought to end the universal threat posed by the Phoenix Force, which had assumed the form of X-Man Jean Grey. The Guard defeated the X-Men, but allowed them to return to Earth after Phoenix seemingly committed suicide.
Later, the exiled Shi'ar Deathbird manipulated the Guard into believing the X-Men had kidnapped her sister, Lilandra. Despite the truth being revealed, Deathbird was able to usurp the throne and forced the Guard to aid her in a search for the powerful "Phalkon", which was revealed to be the Phoenix Force, then wielded by Rachel Summers. In the ensuing clash with the Starjammers and Phoenix's teammates in Excalibur, Deathbird and the Guard were defeated. Later, Deathbird and the Guard were captured by members of the shapeshifting alien Skrulls. Deathbird was able to escape and enlisted the X-Men's aid in defeating the Skrulls, after which she abdicated the throne to Lilandra. However, the Skrulls were able to incite a war between the Shi'ar and the Kree that spilled over into Earth space, resulting in the Guard clashing with the Avengers. The war ended after the Kree population was decimated, leaving Lilandra with no other choice but to conquer the remaining Kree.
During the time when many Earth heroes were believed dead after a battle with the psionic being Onslaught, Lilandra dispatched a cadre of Guardsmen to help protect Earth. There, the Guardsmen uncovered a plot by a militant Kree faction to exact revenge for Earth's involvement in the Kree/Shi'ar war. The Guard ultimately proved triumphant, but not before the Kree's leader, the Supreme Intelligence, was recreated. Soon after, the Guard foiled an assassination attempt on Lilandra by the Kree Ronan and his unwilling agents, the Inhumans' Royal Family.
After Lilandra came under the mental possession of Cassandra Nova, the genetic twin of Xavier who had usurped her brother's body, she was mentally coerced into dispatching the Guard to kill the X-Men. After a pitched battle, the X-Men were able to convince the Guard of the true threat, and together they defeated Nova and freed Lilandra (although not before Nova had been able to do immense damage to the empire).