Calvin Rankin was raised by his father Ronald Rankin, who was experimenting with genetics. Once when Calvin was left alone and caused a lab accident which gave him his copying powers. His father, afraid that others would despise him went into hiding with Calvin in a cave, where his father was building a machine that would take away his powers. The villagers found this out and attacked the Rankins' causing a cave-in, killing Ronald.
Years later while in college Calvin met Hank McCoy and Bobby Drake. He realized after using thier powers that they were Iceman and Beast of the X-Men. He then later was in a shop were Jean Grey was. He developed telekinetic powers and realized that she was Marvel Girl. He then proceeded to follow her back to the Mansion, where he introduced himself and asked to join the X-Men. After revealing his plan to them they tussled until Calvin was able to capture Jean and hold her hostage. Calvin then took her to the cave where his father had died and planned on using the machine his father created to make the powers he copies permanent. Not realizing that it would instead take away his powers he used the machine and became powerless. Xavier then removed his memories of the X-men and Calvin returned to college.
Later during a lab accident in college he regained his powers and memory of the X-Men. Seeking revenge he demanded that he become a member of X-Men. Xavier reluctantly accepted and made Calvin the deputy leader. During the next several missions Calvin faced off against Banshee, Ogre and the Factor Three. After that Calvin was offended by Cyclops and attacked him. Xavier finally fed up with Calvin's attitude kicked him off of the team. Calvin left the mansion later to find the Super-Adaptoid attacking the X-Men. Hoping to become even more powerful Calvin offered to join the Adaptoid in his plan to conquer the earth. But upon learning he would become a mindless pawn, he changed his mind and attacked the Adaptoid, losing his powers in the process.
Calvin then returned to school until his powers started to return. This time however his powers where drawing the life force of those around him. Frightened he fled to Canada were his girlfriend, Vera Cantor asked Hank McCoy to help him in finding a cure. Unfortunately the Hulk felt Calvin's power and sought to destroy the source. As the Hulk grew closer Calvin started to absorb the radiation which gave the Hulk his strength. While the Hulk and Beast fought Calvin absorbed too much radiation and died of poisoning. Calvin was then buried in an undisclosed location.
Years later somehow Calvin absorbed the healing factor and powers of Wolverine and was brought back to life, believing himself to be Wolverine. He again encountered the Hulk and later learned that his father was connected to Weapon X. Calvin then regained his memories and the real Wolverine arranged for Calvin to spend some time in Japan to help learn to control his powers.
Years later in Siberia, X-Force found him and tried to calm him down after they crashed into a station nearby. Sometime later Mimic formed an alliance with Onslaught, who upgraded his powers in exchange for his services. He also allied himself with a man known as Sledge who also upgraded his powers.
Sometime later Excalibur was searching for Xavier after the Operation: Zero Tolerance fiasco and instead found Mimic being held hostage by rogue Sentinels. Confused he attacked the members of Excalibur and ultimately lost. They then took him to their headquarters where he recuperated and attended the wedding of Captain Britain and Meggan.
Weeks later he for some unknown reason joined the new Brotherhood Of Mutants and helped the X-Men defeat Cerebro. He then continued to work with the Brotherhood when they tried to capture X-51 a.k.a. Machine Man. They failed and Calvin was captured. Later while being held prisoner Valerie Cooper came and consoled him and offered him a way out of prison, which he took. He was then alongside the Brotherhood affected by a beam sent down by the High Evolutionary in order to de-power all of Earths mutants. The beam caused Calvin to lose his powers momentarily, but he quickly regained them moments after the beam was reversed.
Recently Calvin was seen as a captive of the Thunderbolts after recent developments as a captive alongside hundreds of other criminals in the Folding Castle Detention Quadrant. It is unknown if Calvin has joined the Thunderbolts or if he is still being held by them as a prisoner.