Mentor is a member of the Imperial Guard, a multi-ethnic group of super-powered alien beings who act as enforcers of the laws of the Shi'ar Empire. Part of the division of the Imperial Guard known as the Superguardians, the super-intelligent Mentor was amongst the first of the Imperial Guard encountered by the team of superhuman mutant adventurers known as the X-Men who sought to rescue the Princess-Majestrix Lilandra from her insane brother, then-Majestor D'ken. Following the orders of their emperor, the Guard clashed with the X-Men and were on the verge of winning when the band of interstellar freebooters known as the Starjammers arrived to turn the tide of battle in the X-Men's favor.
Mentor was later amongst those few Imperial Guard members who opposed the treacherous Shi'ar High Council member Lord Samédàr who was aiding an attempted coup of the Shi'ar throne by Deathbird. Even after many of the Guard chose to side with Samédàr, Mentor remained steadfast in his loyalty to then-Empress Lilandra.
When the Empress Lilandra, having regained her throne, learned of the many Earth heroes that had sacrificed their lives to stop the malevolent psionic being named Onslaught, she dispatched eight members of the Imperial Guard, including Mentor, to protect Earth. While on Earth, the Guard uncovered a plot by a militant Kree faction to simulate a radical political activist group in revenge for Earth's involvement in the Kree/Shi'ar war. In reality, the group created a "nega-reactor", similar to the bomb that was used on the Kree. However, this plot was stopped by the Guard, but not before the reactor was used by the Kree's leader, the Supreme Intelligence, to re-incorporate itself after being presumably killed at the end of the war.
Subsequently, Mentor was amongst those Imperial Guard members who defended Lilandra against an assassination attempt by the Kree Ronan the Accuser and his unwilling agents, the royal family of the Earth race known as the Inhumans.